A/W/J  «     T  QL 


C65 


TV 


thi.s.-  reserved  fur  *|nviul  ref- 

1C,   may    l.i-   ki-pt    for  wri'k   ;m«l 

uv.l   fur  tin-  NMIII,.  time.     This  book   is  .1 
'•rurn.-.l   ,n,   the   last    -latr  stani|>«-,|    l,,>lo\v.       \ 
fin.-   of   li\.-   .-nits   will    In-   clun-^,.,1    fur   ,.;,i-h    da  v 


JAH  521915. 


MAfi  1  2  '5' 


TEXT-BOOKS   IN    BOTANY 

By  John  M.  Coulter,  Ph.D. 

HEAD  OP  DEPARTMENT  OF  BOTANY  IN  THE  UNIVERSITY 
OF   CHICAGO 


Text-Book  of  Botany.  12mo.  Illustrated. 
Cloth $1.25 

Plant  Studies.  An  Elementary  Botany.  12mo. 
Cloth $1.25 

Plant  Relations.  A  First  Book  of  Botany. 
12mo.  Cloth $1.10 

Plant  Structures.  A  Second  Book  of  Bot- 
any. 12mo.  Cloth $1.20 

Plants.  The  two  foregoing  in  one  volume. 
For  Normal  Schools  and  Colleges.  12mo. 
Cloth $1.80 

In  the  Twentieth  Century  Series  of  Text-Books 


D.  Appleton  and  Company,  New  York 


TWENTIETH   CENTURY   TEXT-BOOKS 


A  TEXT-BOOK  OF  BOTANY 


FOR  SECONDARY  SCHOOLS 


BY 
JOHN    M.   COULTER,  A.M.,  PH.D. 

HEAD   OF   DEPARTMENT   OF   BOTANY,    THE   UNIVERSITY 
OF  CHICAGO 


NEW    YORK 

D.    APPLETON    AND    COMPANY 
1909 


COPYRIGHT,  1905,  BY 
D.  APPLETON  AND  COMPANY 


PREFACE 


THE  several  editions  of.  Plant  Studies,  designed  for  use 
in  secondary  schools,  were  combined  abridgments  of  Plant 
Relations  and  Plant  Structures.  Although  this  arrangement 
involved  a  certain  amount  of  repetition  and  lack  of  conti- 
nuity, it  was  felt  that  these  faults  would  be  corrected  by 
the  competent  teacher,  whose  chief  desire  would  be  to 
secure  points  of  view  in  reference  to  botanical  material. 

During  the  five  years  that  have  elapsed  since  the  publi- 
cation of  the  first  edition  of  Plant  Studies,  the  opinions  of 
many  experienced  teachers  have  been  obtained.  These 
opinions  have  been  based  upon  repeated  use  of  the  book, 
and  have  been  of  the  greatest  possible  service  in  develop- 
ing definite  ideas  as  to  the  adjustment  of  the  subject  to  the 
needs  of  the  schools.  The  natural  outgrowth  of  this  co- 
operation between  author  and  teachers  has  been  the  prep- 
aration of  the  present  Text-Book  of  Botany,  which  seeks  to 
express  their  combined  judgment.  There  has  been  substan- 
tial agreement  as  to  the  nature  of  the  material  and  the 
points  of  view,  the  only  differences  of  opinion  being  such 
minor  ones  of  presentation  as  must  always  be  found  among 
equally  competent  teachers. 

There  has  been  no  attempt  to  treat  the  various  divisions 

T 


310808 


vi  PREFACE 

of  Botany  separately,  but  rather  to  develop  them  all  in  their 
most  natural  relationships;  and  yet  morphology,  physiology, 
and  ecology  have  been  kept  so  distinct  that  the  teacher  will 
have  no  difficulty  in  calling  attention  to  these  divisions,  if  it 
is  thought  desirable. 

In  the  first  five  chapters  the  structure,  function,  and  rela- 
tionships of  the  most  obvious  plant  organs  are  considered. 
The  purpose  has  been  to  use  the  most  easily  observed  ma- 
terial to  give  preliminary  training  in  observation  and  some 
conception  of  the  activities  of  plants. 

The  following  thirteen  chapters  present  an  outline  of  the 
plant  kingdom  in  the  simplest  possible  form  to  be  at  all  ade- 
quate. In  these  chapters  the  morphological  point  of  view 
necessarily  dominates,  but  not  to  the  exclusion  of  the  phys- 
iological and  ecological.  In  this  presentation  of  the  great 
groups,  which  is  also  an  outline  of  classification,  there  have 
been  included  special  accounts  of  forms  of  economic  interest ; 
not  only  because  such  forms  as  well  as  any  others  may 
illustrate  groups,  but  chiefly  because  there  is  a  growing  con- 
viction that  Botany  in  the  schools  must  relate  pupils  to  their 
common  experiences,  as  well  as  train  them  in  science.  For 
the  same  general  reason  the  brief  chapters  on  plant-breeding 
and  forestry  have  been  introduced. 

The  four  closing  chapters  include  a  very  brief  account  of 
plant  associations,  the  most  inclusive  view  of  plants.  This 
subject  is  merely  introduced  rather  than  developed. 

It  cannot  be  repeated  too  often  that  this  book  will  not 
serve  its  purpose  unless  it  is  used  as  a  supplement  to  the 
teacher,  to  the  laboratory,  and  to  field-work.  Furthermore 
it  must  be  insisted  that  the  sequence  of  the  book  need  not  be 


PREFACE  vii 

the  sequence  used  by  the  teacher.  For  example,  work  on 
leaves,  stems,  roots,  and  seeds  may  come  in  any  order,  and 
may  well  differ  according  to  the  availability  of  material  or  the 
conviction  of  the  teacher.  It  so  happens  that  the  book  begins 
with  leaves,  but  those  teachers  who  prefer  to  begin  with  seeds 
should  do  so. 

In  the  matter  of  illustrations,  there  have  been  many  im- 
provements, eliminations,  and  additions.  All  of  this  work 
has  been  done  or  directed  by  my  assistant,  Dr.  W.  J.  G.  Land, 
whose  skill  in  photography  has  been  made  use  of  freely  and 
whose  cooperation  has  added  much  to  the  value  of  the  book. 
Unless  otherwise  credited,  all  illustrations  have  been  prepared 
for  this  volume  or  those  previously  mentioned. 

JOHN  M.  COULTER. 

THE  UNIVERSITY  OP  CHICAGO, 
September,  1905. 


CONTENTS 


CHAPTER  PAGE. 

I. — INTRODUCTION 1 

II. — LEAVES 5 

III.— STEMS II 

IV.— ROOTS 71 

V. — GERMINATION  OF  Si  84 

VI.— ALG^ .98 

VII.— FUNGI 129 

VIII.— LIVERWORTS 165 

IX.— MOSSES 175 

X .  -FERNS 183 

XI.       IlnlfSKTAILS   AND  CLUK-M»»I .s          .....    197 

XII. — GYMNOSPERMS 207 

XIII. — ANGIOSPERMS 220 

XIV. — FLOWERS  AND  INSECTS 212 

XV. — SEED  DISPERSAL     ........  -•'>•"> 

XVI. — MONOCOTYLEDONS -<>- 

XVII. — DICOTYLEDONS:  ARCHICHLAMYDE.E         ....  282 

XVIII. — DICOTYLEDONS  :  SYMPETAL.E 302 

XIX. — PLANT-BREEDING 316 

XX— FORESTRY 320 

X  X  I. — PLANT  ASSOCIATIONS      .......  324 

XXII.— HYDROPHYTES 328 

XXIII.— XEROPHYTES 337 

XXIV.— MESOPHYTES 345 

INDEX  .  357 


A  TEXT-BOOK  OF  BOTANY 

FOR  SECONDARY   SCHOOLS 


CHAPTER  I 

INTRODUCTION 

1.  Occurrence  of  plants. — Plants  form  the  natural  cover- 
ing of  the  earth's  surface.     So  generally  is  this  true  that  a 
land  surface  without  plants  seems  remarkable.     Not  only 
do  plants  cover  the  land,  but  they  abound  in  waters  as  well, 
both  fresh  and  salt  waters.     One  of  the  most  noticeable 
facts  in  regard  to  the  occurrence  of  plants  is  that  they  do 
not  form  a  monotonous  covering  for  the  earth's  surface, 
but  that  there  are  forests  in  one  place,  meadows  in  another, 
swamp  growths  in  another,  etc.     In  this  way  the  general 
appearance  of  vegetation  is  exceedingly  varied,  and  each 
appearance  tells  of  certain  conditions  of  living. 

2.  Plants   as   living   things. — It   is  very   important   to 
begin  the  study  of  plants  with  the  knowledge  that  they  are 
alive  and  at  work.     It  must  not  be  thought  that  animals 
are  alive  and  plants  are  not.     There  is  a  common  impression 
that  to  be  alive  means  to  have  the  power  of  locomotion, 
but  this  is  far  from  true;  and  in  fact  some  plants  have  the 
power  of  locomotion  and  some  animals  do  not.     Both  plants 
and  animals  are  living  forms,  and  the  lawrs  of  living  that 
animals  obey  must  be  obeyed  also  by  plants.     Of  course 
there  are  differences  in  detail,  but  the  general  principles 
of  living  are  the  same  in  all  living  forms.     To  begin  with  the 

1 


2  A  TEXT-BOOK  OP  BOTANY 

thought  that  plants  are  alive  and  at  work  is  important 
because  this  fact  gives  meaning  to  their  forms  and  structures 
and  positions.  For  example,  the  structure  of  a  leaf  has  no 
meaning  until  it  is  discovered  how  its  structure  enables  the 
leaf  to  do  its  work. 

3.  The  plant  body. — Every  plant  has  a  body,  which  may 
be  alike  throughout  or  may  be  made  up  of  a  number  of 
different  parts.     If  one  part  of  the  body  does  not  differ  from 
another,  the  plant  is  said  to  be  simple;  but  the  most  con- 
spicuous plants,  those  with  which  every  one  is  best  ac- 
quainted, are  made  up  of  dissimilar  parts,  such  as  root, 
stem,  and  leaf,  and  such  plants  are  said  to  be  complex. 
Simple  and  complex  plants  do  the  same  work;  but  in  the 
simple  plant  the  whole  body  does  every  kind  of  work,  while 
in  the  complex  plant  different  kinds  of  work  are  done  by 
different  regions  of  the  body,  and  these  regions  come  to  look 
unlike  when  different  shapes  are  better  suited  to  different 
kinds  of  work,  as  in  the  case  of  leaf  and  root. 

4.  Plant  organs. — The   different   regions  of  the   plant 
body  thus  set  apart  for  special  purposes  are  called  organs; 
and  complex  plants  have  several  kinds  of  organs,  just  as  the 
human  body  has  hands,  feet,  eyes,  etc.     The  advantage  of 
this  to  the  plant  becomes  plain  by  using  the  common  illus- 
tration of  the  difference  between  a  tribe  of  savages  and  a 
civilized  community.     The  savages  all  do  the  same  things, 
and  each  savage  does  everything.     In  the  civilized  com- 
munity some  of  the  members  are  farmers,  others  bakers, 
others    tailors,  others    butchers,    etc.     This    is  known   as 
"division  of  labor,"  and  one  great  advantage  it  has  is  that 
every  kind  of  work  is  better  done.     Several  kinds  of  organs 
in  a  plant  mean   to  the  plant  just  what  division  of  labor 
means  to  the  community;  it  results  in  better  work  and  more 
work. 

5.  Plant  work.  —Although  many  different  kinds  of  work 
are  being  carried  on  by  plants,  all  the  work  may  be  put 


INTRODUCTION  3 

under  two  heads:  nutrition  and  reproduction.  This  means 
that  every  plant  must  care  for  two  things:  (1)  the  support  of 
its  own  body  (nutrition)  and  (2)  the  production  of  other 
plants  like  itself  (reproduction).  To  the  great  work  of 
nutrition  many  kinds  of  work  contribute,  and  the  same  is 
true  of  reproduction.  In  a  complex  plant,  therefore,  there 
are  nutritive  organs  and  reproductive  organs;  and  this 
means  that  there  are  certain  organs  which  specially  con- 
tribute to  the  work  of  nutrition,  and  others  which  are 
specially  concerned  with  the  work  of  reproduction.  It 
must  not  be  supposed  that  an  organ  is  necessarily  limited 
to  one  kind  of  work.  Its  form  and  structure  fit  it  for  a 
particular  kind  of  work,  which  may  be  called  its  specialty; 
but  it  is  not  excluded  from  other  kinds  of  work,  just  as 
a  man  who  is  specially  trained  to  be  a  carpenter  may  do 
other  things  also. 

6.  Life-relations. — In  all  of  its  work  a  plant  is  very  de- 
pendent upon  its  surroundings.  For  example,  it  must 
receive  material  from  the  outside  and  get  rid  of  waste 
material.  Therefore,  organs  must  establish  certain  definite 
relations  with  things  outside  of  themselves  before  they  can 
work  effectively;  and  these  necessary  relations  are  known 
as  life-relations.  For  example,  green  leaves  are  definitely 
related  to  light — they  cannot  do  their  peculiar  work 
without  it;  many  roots  must  be  related  to  the  soil;  certain 
plants  are  related  to  abundant  water;  some  plants  are  re- 
lated to  other  plants,  as  parasites,  etc.  It  is  evident  that  a 
plant  with  several  organs  may  hold  a  great  variety  of  life- 
relations,  and  it  is  a  very  complex  problem  for  such  a  plant 
to  adjust  all  of  its  parts  properly  to  their  most  effective 
relations.  It  must  not  be  supposed  that  even  a  single  organ 
holds  a  perfectly  simple  life-relation,  for  it  is  affected  by  a 
great  variety  of  things.  For  example,  a  root  is  affected  by 
gravity,  moisture,  soil  material,  contact,  etc.  Each  organ, 
therefore,  must  become  adjusted  to  a  complex  set  of  rela- 


4  A  TEXT-BOOK  OF  BOTANY 

tions;  and  a  plant  with  several  organs  has  so  many  delicate 
adjustments  to  care  for  that  it  is  impossible,  as  yet,  for  us 
to  explain  why  all  of  its  parts  are  placed  just  as  they  are. 

7.  Some  conspicuous  organs. — The  prominent  plants, 
which  are  spoken  of  as  herbs,  shrubs,  and  trees,  have  three 
conspicuous  organs,  root,  stem,  and  leaf,  which  are  con- 
cerned with  nutrition;  and  most  of  these  plants  have  at 
some  time  also  another  structure,  the  flower,  which  is  con- 
cerned with  reproduction.  Our  first  attention  will  be  given 
to  these  three  great  nutritive  organs.  A  tree,  for  example, 
has  its  roots  extending  more  or  less  widely  through  the  soil; 
from  the  roots  a  stem  rises  into  the  air  and  branches  more  or 
less  extensively;  and  upon  this  stem  or  its  branches  leaves 
are  borne.  Such  is  the  general  plan  of  the  more  complex 
plants;  and  our  first  purpose  will  be  to  discover  what  these 
organs  are  doing,  and  why  they  are  so  related  to  one  another 
and  to  their  surroundings. 


CHAPTER  II 

LEAVES 

8.  Arrangement. — Leaves  appear  upon  the  stems  at 
definite  regions  called  nodes  (joints);  and  this  jointed 
structure  of  the  stem  is  one  of  its  characteristic  features, 
although  it  is  much  more  conspicuous  in  some  plants  than 


FIG.   1. — Leaf  arrangement:     A,  spiral  or  alternate  .eaves;   B,  opposite   (cyclic) 
leaves;  C,  whorled  (cyclic)  leaves. — After  GRAY. 

in  others.  In  certain  plants  only  one  leaf  appears  at  each 
node;  and  if  an  imaginary  line  be  drawn  connecting  the 
points  on  the  nodes  at  which  successive  leaves  appear,  it 

5 


6  A  TEXT-BOOK  OF   BOTANY 

will  form  a  spiral  winding  about  the  stem  (Fig.  1,  ^4).  As  a 
consequence,  leaves  with  this  arrangement  are  said  to  be 
spiral,  though  they  are  still  often  called  alternate.  On 
account  of  this  spiral  arrangement,  two  successive  leaves  are 
in  different  vertical  planes,  and  the  danger  of  the  upper  leaf 
shading  the  lower  is  reduced.  In  other  plants  two  or  more 
leaves  appear  at  each  node;  and  as  an  imaginary  line  con- 
necting their  points  of  origin  forms  a  circle  about  the  stem, 
the  arrangement  is  called  cyclic.  Very  commonly,  however, 
when  two  leaves  appear  at  a  node  they  are  said  to  be 
opposite  (Fig.  1,  B);  and  when  more  than  two  appear  they 
are  described  as  whorled  (Fig.  1,  C).  The  cycle  of  leaves  at 
one  node  does  not  stand  directly  over  the  cycle  at  the  node 
below,  but  over  the  spaces  between  the  lower  leaves,  the 
danger  of  shading  being  reduced  as  in  the  case  of  the  spiral 
arrangement.  In  fact,  the  cyclic  arrangement  differs  from 
the  spiral  only  in  having  two  or  more  parallel  spirals. 

9.  Regions. — The  conspicuous  part  of  a  leaf  is  the  ex- 
panded portion  known  as  the  blade,  and  often  the  leaf  is  all 
blade.     In  many  cases  the  leaf  has  a  stalk  (petiole)  which 
bears  the  blade  more  or  less  away  from  the  stem;  and  in 
certain  groups  of  plants  a  third  region  is  evident,  usually 
consisting  of  a  pair  of  more  or  less  blade-like  appendages 
(stipules)  on  the  petiole  where  it  joins  the  stem  (Fig.  2,  A). 
As  might  be  expected,  the  essential  part  of  the  leaf  is  the 
blade,  and  ordinarily  when  the  word  leaf  is  used  it  refers  to 
the  blade. 

10.  Venation. — Upon  examining  an  ordinary  leaf,  the 
blade  is  seen  to  consist  of  a  green  substance  through  which 
a  network  of  veins  is  variously  distributed      The  larger 
veins  that  enter  the  blade  send  off  smaller  branches,  and 
these  send  off  still  smaller  ones,  until  the  smallest  veinlets 
are  invisible.     This  is  plainly  shown  by  a  skeleton  leaf; 
that  is,  one  which  has  been  so  treated  that  all  the  green 
substance  has  disappeared,  and  only  the  network  of  veins 


LEAVES  7 

remains.  The  vein-system  or  venation  of  leaves  is  ex- 
ceedingly diverse,  but  all  forms  can  be  referred  to  a  few 
general  plans. 

In  some  leaves  a  single  very  prominent  vein  runs  through 
the  middle  of  the  blade,  and  is  called  the  midrib.  From 
this  all  the  minor  veins  arise  as  branches,  and  such  a  leaf  is 
said  to  be  pinnately  veined  (Fig.  2,  A,  and  Fig.  9).  In  other 
leaves  several  large  veins  (ribs)  of  equal  prominence  enter 
the  blade  and  diverge,  each  giving  rise  to  smaller  branches. 


FIG.  2. — Venation:  A,  pinnately  veined  leaf  of  quince,  showing  blade,  petiole, 
and  stipules  ;  /?,  palmately  veined  leaf  of  geranium  ;  C,  parallel-veined  leaf  of 
lily-of-the-valley. — After  GRAY. 

Such  a  leaf  is  said  to  be  palmately  veined  (Fig.  2,  B,  and  Fig. 
16).  In  still  other  leaves  all  the  visible  veins  run  ap- 
proximately parallel  from  the  base  of  the  blade  to  its  apex, 
such  leaves  being  parallel-veined  (Fig.  2,  C),  as  distinct  from 
the  two  preceding,  which  are  both  net-veined. 

1 1 .  Form. — The  forms  of  leaves  are  exceedingly  varied 
and  are  related  to  their  venation.     Palmately  veined  leaves 


8 


A   TEXT-BOOK  OF  BOTANY 


incline  to  broader  forms  than  leaves  pinnately  veined  or 
parallel-veined.  Names  have  been  given  to  the  various  leaf 
forms,  as  linear,  lanceolate,  ovate,  orbicular,  etc.,  but  they 
can  be  learned  as  they  are  needed.  In  the  net- veined 
leaves  the  margin  of  the  blade  may  be  more  or  less  deeply 
toothed  br  lobed  (Fig.  2,  B) ;  but  in  the  parallel-veined  leaves 

the  margin  is  not  at  all 
toothed,  in  which  case 
the  leaf  is  said  to  be  en- 
tire (Fig.  2,  C).  It  is 
quite  common  also  for 
net-veined  leaves  to 
branch,  when  they  are 
said  to  be  compound. 
In  this  case  the  leaf- 
blade  is  broken  up 
into  a  number  of  small 
blades,  sometimes  very 
many  of  them,  called 
leaflets.  A  branching 
pinnate  leaf  is  said  to 
be  pinnately  compound 
(Fig.  3,  A);  and  a 
branching  palmateleaf, 
palmately  compound 
(Fig.  3,5). 

12.  Exposure  to  light. — The  special  work  of  leaves  is  ex- 
ceedingly important,  and  this  work  cannot  be  done  unless 
the  leaf  is  exposed  to  light.  This  fact  explains  many 
things  in  connection  with  the  position  and  arrangement 
of  leaves.  Leaves  must  be  arranged  to  receive  as  much  light 
as  possible  to  help  in  their  work,  but  too  intense  light  is 
dangerous;  hence  the  adjustment  to  light  is  a  delicate  one. 
The  exact  position  any  particular  leaf  holds  in  relation  to 
light,  therefore,  depends  upon  many  circumstances,  and 


FIG.  3. — Compound  leaves:  .4,  pinnately  com- 
pound leaf  of  black  locust ;  B,  palmately  com- 
pound leaf  of  red  clover,  with  three  leaflets, 
also  showing  stipules. 


LEAVES 


0 


cannot  be  covered  by  a  general  rule,  except  that  it  seeks 
to  get  all  the  light  it  can  without  danger.  How  leaves  seek 
the  light  will  be  first  considered,  and  later  how  they  protect 
themselves  against  it. 

(1)  Horizontal  position. — The  ordinary  position  of  the 
leaf  is  more  or  less  horizontal.  This  enables  it  to  receive 
the  direct  rays  of  light  upon  its  upper  surface,  and  more 
rays  strike  it  than  if  it  stood  obliquely  or  on  edge.  Most 
leaves  when  fully  grown  are  in  a  fixed  position  and  cannot 
change  it,  however  unfavorable  it  may  become;  but  there 


FIG.  4. — Geranium  leave-  *-\|.i»f>il   first   to  vertical   (A)  and   then  to  oblique  (B) 

rays  of  light. 

are  leaves  so  constructed  that  they  can  shift  their  position 
as  the  direction  of  the  light  changes,  or  the  stem  bearing 
the  leaves  may  shift  its  position  so  that  a  better  relation  to 
light  is  secured  (Fig.  4).  If  a  garden  nasturtium  growing  in 
a  window  be  observed,  its  leaves  will  be  seen  facing  the 


10 


A  TEXT-BOOK  OF  BOTANY 


light;  but  if  it  be  turned  around  so  as  to  bring  the  other 
side  of  the  plant  to  the  light,  the  leaves  will  become  adjusted 
gradually  to  the  new  direction.  Many  plants  have  more 
or  less  power  to  direct  their  leaves,  and  it  would  be  in- 
teresting to  observe  what  common  plants  of  any  region 
possess  it.  ^ 

(2)  Problem  of  shading. — It  is  evident  that  leaves  of  the 
same  plant  are  in  danger  of  shading  one  another;  and  while 

it  cannot  always  be  pre- 
vented, there  are  ways  by 
which  the  danger  is  dimin- 

"****  """^SSBI  ished.     The  problem  of  the 

ttl^^TKPxL  plant  is  to  develop  as  much 

leaf  surface  as  possible  and 
to  place  it  in  the  most  fa- 
vorable position  for  work. 
The  spiral  arrangement  of 
leaves  prevents  two  suc- 
cessive leaves  standing  in 
the  same  plane,  and  results 
in  vertical  rows  of  leaves 
distributed  about  the  stem. 
The  narrower  the  leaves, 
the  more  numerous  may 
be  the  vertical  rows;  and 
the  broader  the  leaves,  the 
fewer  the  vertical  rows 
(Fig.  5).  In  many  herbs 
whose  leaves  are  rather 
large  and  close  together, 

FIG.  5.— A  broad-leaved  plant,  showing  the  petioles  of  the  lower 
few  vertical  rows,  and  variously  directed  leaves  are  USUally  longer 
leaves. 

than     those     above,     and 

thus  their  blades  are  thrust  beyond  the  shadow.  The 
same  result  is  obtained  when  the  lowest  leaves  of  a  plant 


LEAVES 


11 


are  the  largest,  and  the  upper  leaves  gradually  diminish 
in  size. 

(3)  Rosette-habit. — An  extreme  case  of  crowding  is  shown 
by  plants  with  the  rosette-habit :  that  is,  those  which  produce 


FIG.  6.— Rosette-habit  shown  by  mullein  (4)  and  evening-primrose  (5). 

a  cluster  or  rosette  of  leaves  at  the  base  of  the  stem  (Figs. 
0  and  7).  Often  this  rosette,  frequently  lying  flat  upon  the 
ground  or  upon  the 
rocks,  includes  all 
the  leaves  the  plant 
produces.  This  close 
overlapping  of  leaves 
is  a  poor  adjustment 
to  light  at  best,  but 
there  is  evident  an 
adjustment  to  se- 
cure the  most  light 
possible  under  the 
circumstances.  The 
lowest  leaves  of  the 
rosette  are  the  long- 
est, and  the  upper  ones  become  gradually  shorter,  so  that 
each  leaf  has  at  least  a  part  of  its  surface  exposed  to  light. 


12 


LEAVES 


13 


The  overlapped  base  is  not  expanded  so  much  as  the  ex- 
posed apex,  and  hence  such  leaves  are  usually  narrow 
toward  the  base  and  broad  toward  the  apex.  This  nar- 
rowing at  the  base  is  sometimes  carried  so  far  that  most 
of  the  overlapped  part  is  only  a  petiole. 

(4)  Leaf-mosaics. — All  leaf  adjustments  (including  the 
spiral  arrangement,  elongation  of  lower  petioles,  etc.) 
that  have  to  do  with  fitting  leaf-blades  together,  so  that  the 
greatest  amount  of  leaf  surface  may  be  exposed  to  direct 
illumination,  may  be  regarded  as  concerned  in  the  con- 


Fin.  9. — Leaves  of  Fittonia  showing  mosaic  arrangement. 

st ruction  of  a  leaf-mosaic.  A  general  mosaic  arrangement 
of  leaves  may  be  observed  in  connection  with  almost  every 
broad-leaved  plant  (Figs.  8  and  9) ;  and  even  when  the 
leaves  are  separated  along  an  erect  stem,  a  view  from  above, 


14 


LEAVES  15 

in  which  all  the  leaves  are  referred  to  a  single  plane,  shows 
the  mosaic.  In  many  trees  in  dense  forests,  notably  in 
the  tropics,  the  leaves  appear  chiefly  and  sometimes  ex- 
clusively at  the  extremities  of  the  branches,  often  producing 
a  magnificent  dome-like  mosaic. 

In  the  case  of  stem-  exposed  to  direct  light  only  on  one 
side,  as  the  horizontal  branches  of  trees,  stems  prostrate 
on  the  ground,  and  stems  against  a  support  (as  climbers 
and  twiners),  the  leaf-i>lades  must  be  brought  to  the  light 
side  so  far  as  possible,  and  those  that  belong  to  the  shaded 
side  must  be  fitted  into  the  spaces  left  by  those  that  belong 
to  the  illuminated  side.  This  is  brought  about  in  various 
ways,  as  by  the  twisting  of  the  stem,  the  twisting  and 
elongation  of  the  petiole,  the  bending  of  the  blade  on  the 
petiole,  etc.  Looking  up  into  a  tree  in  full  foliage,  one 
will  notice  that  the  horizontal  branches  are  comparatively 
bare  beneath,  the  leaf-blades  being  displayed  on  the  upper 
side  as  a  mosaic.  The  most  complete  leaf-mosaic  is  shown 
by  certain  ivies,  involving  such  an  amount  of  twisting,  dis- 
placement, elongation  of  petioles,  etc.,  as  to  give  ample 
evidence  of  the  importance  of  securing  for  leaves  an  ex- 
posure to  light  (Fig.  10). 

13.  Structure. — Before  considering  the  work  of  the  leaf 
it  will  be  necessary  to  know  something  of  its  minute 
structure.  To  see  this  structure,  not  merely  surface  views 
must  be  obtained,  but  also  good  clear  sections  through  the 
leaf  (cross-sections)  must  be  made;  and  for  this  purpose  a 
relatively  thick  spongy  leaf,  like  that  of  the  hyacinth  or 
the  lily,  gives  the  least  trouble. 

(1)  Epidermis. — It  is  possible  to  peel  off  from  the  sur- 
face of  such  a  leaf  a  delicate  transparent  skin  (epidermis}. 
This  epidermis  completely  covers  the  leaf,  and  generally 
shows  no  green  color.  Examined  under  the  compound 
microscope  it  is  seen  to  be  made  up  of  small  units  of 
structure  known  as  cells  (Fig.  11).  Each  cell  is  bounded 


16 


A   TEXT-BOOK  OF  BOTANY 


by  a  wall,  and  in  the  epidermis  these  cells  fit  closely  to- 
gether, sometimes  dovetailing  with  one  another. 

Characteristic  openings  in  the  epidermis  also  will  be  dis- 
covered, sometimes  in  very  great  numbers.  Guarding  each 
slit-like  opening  are  two  crescent-shaped  epidermal  cells, 
called  guard-cells  (Fig.  11).  The  whole  apparatus  is  known 
as  a  stoma  (plural  stomata),  which  really  means  "mouth," 
of  which  the  guard-cells  might  be  thought  of  as  the  lips. 
One  important  fact  about  stomata  is  that  the  guard-cells 
can  change  their  shape,  and  so  vary  the  size  of  the  opening. 
These  numerous  openings  are  passageways  into  the  interior 
of  the  leaf,  putting  the  internal  cells  into  communication 

with  the  air  out- 
side, and  so  fa- 
cilitating the  in- 
terchange of  gases 
that  will  be  de- 
scribed later  in 
connection  with 
the  work  of  the 
leaf.  In  horizon- 
tal leaves  the  sto- 
mata are  chiefly 
and  sometimes  ex- 
clusively on  the 
lower  surface,  a 
fair  average  number  being  about  100  to  each  square  milli- 
meter of  surface  (about  62,500  to  the  square  inch) ;  although 
in  some  cases  the  number  may  reach  700  to  the  square  milli- 
meter (almost  450,000  to  the  square  inch).  In  leaves 
exposed  alike  on  both  sides  to  the  light,  as  in  the  erect 
leaves  of  the  common  flag,  the  stomata  are  equally  dis- 
tributed on  both  surfaces.  In  floating  leaves,  as  those  of 
water-lilies,  the  stomata  are  all  on  the  upper  surface;  and  in 
submerged  leaves  there  are  no  stomata.  From  this  dis- 


FIG.  11.— Surface  view  of  the  epidermis  of  a  hyacinth 
leaf:  A,  epidermal  cells  and  four  stomata  with  their 
guard-cells  ;  B,  enlarged  view  of  a  single  stoma. 


LEAVES 


17 


tribution  it  is  evident  that  stomata  are  definitely  related  to 
air;  and  that  where  there  is  difference  of  illumination  on  the 
two  surfaces  they  occur  chiefly  on  the  less  illuminated  sur- 
face. Stomata  are  not  peculiar  to  the  epidermis  of  leaves; 
for  they  are  found  in  the  epidermis  of  any  green  part,  as 
young  stems,  fruit,  etc.,  and  even  on  the  colored  parts  of 
flowers. 

(2)  Mesophyll. — A  cross-section  of  a  leaf  such  as  that  of 
the  lily  shows  the  single  layer  of  epidermal  cells  bounding 
the  section  above 
and  below,  pierced 
here  and  there  by 
stomata,  recognized 
by  their  guard-cells 
(Fig.  12).  An  en- 
larged view  of  a  sec- 
tion of  a  single  sto- 
ma  may  be  seen  in 
Fig.  20.  Between 
these  two  epidermal 
layers  is  the  mass 
of  green  tissue  mak- 
ing up  the  body  of 
the  leaf,  and  known 
as  mesophylL  This 
comprises  cells  con- 
taining the  numer- 
ous small  green 
bodies  (chloroplasts) 
that  give  color  to  the  whole  leaf.  Usually  the  mesophyll 
cells  are  arranged  differently  in  the  upper  and  lower  regions 
of  the  horizontal  leaf.  In  the  upper  region  the  cells  just 
beneath  the  epidermis  are  elongated  at  right  angles  to  the 
surface  of  the  leaf,  and  stand  in  close  contact,  forming  the 
palisade  tissue.  In  the  lower  region  of  the  leaf  the  cells 


FIG.  12. — Cross-section  of  a  lily  leaf,  showing  epi- 
dermal layers  <>>  with  stomata  («)  ;  mesophyll 
made  up  of  palisade  tissue  (p)  and  spongy  tissue 
(«p)  with  air-spaces  (a),  and  containing  chloro- 
plasts ;  and  sections  of  veinlets  (r) 


18  A   TEXT-BOOK  OF  BOTANY 

are  irregular  in  form,  and  so  loosely  arranged  as  to  leave 
air-spaces  between  the  cells,  the  whole  region  forming  the 
spongy  tissue  (Fig.  12).  The  air-spaces  communicate  with 
one  another,  thus  forming  a  labyrinthine  system  of  air- 
chambers  throughout  the  spongy  mesophyll.  It  is  into 
this  system  of  air-chambers  that  the  stomata  open,  and 
thus  what  may  be  called  an  internal  atmosphere  is  in  con- 
tact with  all  the  green  working  cells,  and  this  internal 
atmosphere  is  in  free  communication  through  the  stomata 
with  the  external  atmosphere.  The  significance  of  the 
palisade  arrangement  will  be  considered  under  the  head  of 
leaf  protection. 

(3)  Veins. — In  the  cross-section  of  the  leaf  there  will 
be  seen  also  here  and  there,  embedded  in  the  mesophyll, 
the  cross-sections  of  veins  and  veinlets,  that  constitute  the 
supporting  framework  of  the  leaf  and  conduct  material  to 
and  from  the  green  working  cells  (Fig.  12). 

14.  Photosynthesis. — The  peculiar  work  of  green  plants 
or  green  parts  of  plants  is  to  manufacture  the  kind  of  food 
best  known  as  sugars  and  starch,  such  foods  being  called 
carbohydrates.  This  manufacture  is  exceedingly  important, 
for  all  life  is  dependent  upon  it.  If  green  plants  should  stop 
the  manufacture  of  carbohydrates,  the  food  supply  of  the 
world  would  soon  be  exhausted.  All  other  forms  of  food 
are  derived  from  carbohydrates  in  some  way,  and  only  green 
plants  can  add  to  the  stock  that  is  being  drawn  upon  con- 
tinually. This  means  that  green  plants  must  manufacture 
carbohydrates  not  only  for  their  own  use,  but  also  for  the 
use  of  animals  and  of  plants  that  are  not  green.  Since 
leaves  are  chiefly  expansions  of  green  tissue,  they  are  con- 
spicuous in  the  manufacture  of  carbohydrates;  but  it  must 
be  remembered  that  the  manufacture  goes  on  wherever 
there  is  green  tissue,  whether  it  is  found  in  leaves  or  not. 

A  very  conspicuous  fact  about  this  manufacture  is  that 
it  cannot  go  on  unless  the  green  tissue  is  exposed  to  light. 


LEA VMS  J9 

This  explains  why  leaves  arv  <i(iju>trd  in  go  many  ways  to 
obtain  light,  as  described  in  §  12.  It  also  gives  name  to 
the  process,  photosynthesis,  the  name  indicating  that  the 
work  is  done  in  the  presence  of  light. 

The  process  demands  that  carbohydrates  shall  be  made 
from  raw  materials  common  in  nature  and  easily  obtained 
by  plants,  and  in  photosynthesis  two  such  substances  are 
used.  One  of  these  is  water,  which  in  the  plants  com- 
monly thought  of  is  absorbed  by  the  roots  from  the  soil, 
passes  up  through  the  stem,  and  reaches  the  green  working 
cells  of  the  leaves  through  the  veins.  The  other  substance 
is  carbon  dioxide,  a  gas  present  in  small  proportion  in  the  air 
(really  in  the  form  of  carbonic  acid  gas),  but  one  which  is 
being  constantly  renewed  as  it  is  used,  so  that  it  is  always 
available.  Water  is  made  up  of  one  part  of  oxygen  and  two 
parts  of  hydrogen;  while  carbon  dioxide  consists  of  two 
parts  of  oxygen  and  one  part  of  carbon.  These  are  just  the 
elements  that  enter  into  the  structure  of  a  carbohydrate. 

In  photosynthesis  the  elements  of  water  and  carbon 
dioxide  are  separated  and  recombined  to  form  a  carbo- 
hydrate, and  when  this  has  been  accomplished  it  is  found 
that  some  oxygen  has  been  left  over.  That  is,  in  the 
process  oxygen  is  a  waste  product  and  is  given  off  by  the 
working  cells.  Therefore,  in  the  sunlight  a  leaf  is  absorbing 
carbon  dioxide  and  giving  off  oxygen;  and  this  gas  exchange 
is  the  superficial  indication  that  photosynthesis  is  going  on. 

It  is  very  easy  to  discover  that  oxygen  is  being  given 
off  by  a  leaf  exposed  to  light,  and  that  the  amount  given 
off  (and  hence  the  amount  of  work)  depends  upon  the 
intensity  of  the  light.  If  an  actively  growing  water-plant, 
submerged  in  water  in  a  glass  vessel,  be  exposed  to  bright 
light,  bubbles  may  be  seen  coming  from  the  plant  and 
rising  through  the  water  (Figs.  13  and  14).  Shading  the 
vessel  diminishes  the  number  of  bubbles.  That  the  gas 
being  given  off  is  mainly  oxygen  may  be  proved  by  invert- 


20 


LEAVES 


21 


ing  over  the  plants  a  large  funnel  and  leading  the  bubbles 
into  a  test  tube,  in  which  the  presence  of  oxygen  can  then 
be  tested. 

It  has  been  noted  that  photo- 
synthesis is  associated  not  mere- 
ly with  light  but  also  with  green 
tissue  ;  and  in  examining  the 
structure  of  the  leaf  it  was  dis- 
covered (§13)  that  the  green 
color  is  due  to  the  presence  of 
chloroplasts  in  the  mesophyll 
cells.  It  is  these  chloroplasts 
that  manufacture  the  carbo- 
hydrates, and  they  obtain  irom 
the  light  the  power  (energy)  to 
do  it.  The  first  visible  product 
of  photosynthesis  is  starch,  and 
when  the  working  cells  are  very 
active  starch  may  be  observed 
to  accumulate  in  them ;  but  when  the  process  becomes 

slower  or  stops,  as  during  the 
night,  this  starch  disappears,  the 
food  being  carried  away  for  use 
(Figs.  15  and  16).* 

A  summarized   statement  of 
photosynthesis  is  as  follows:  It  is 
the  manufacture  of  carbohydrates 
by  chloroplasts  in  the  presence  of 
FIG.  16.— A  geranium  leaf,  one-    nght,  water  and  carbon  dioxide 
half  of  which  has  been  cov-    being    used,    and   oxygen    beinsr 

ered  ;  the  test  shows   absence  *  ° 

of  starch  in  the  covered  half.          given  OH   as  a  Waste  product. 

*  Experiments  should  be  devised  to  test  for  the  accumulation  of 
starch  in  leaves  that  have  been  exposed  for  some  time  to  a  strong  light, 
and  to  show  that  this  accumulation  does  not  take  place  in  the  dark. 
In  the  experiments  illustrated  by  Figs.  15  and  16,  the  test  for  starch  was 


FIG.  15. — A  bean  leaf  whose  termi- 
nal leaflet  has  been  covered  and 
whose  lateral  leaflets  have  been 
exposed  to  light ;  the  test  shows 
an  absence  of  starch  in  the 
former  and  an  abundance  of  it 
in  the  latter. 


22  A  TEXT-BOOK  OF  BOTANY 

15.  Transpiration. — Water  is  being  evaporated  con- 
stantly from  the  surface  of  a  living  plant  exposed  to  the  air. 
This  loss  of  water  by  the  plant  has  been  called  transpiration. 
Since  leaves  are  especially  exposed  to  the  air,  their  transpira- 
tion is  conspicuous.  Although  the  epidermis  impedes  trans- 
piration, we  have  seen  (§  13)  that  the  leaf  has  in  its  system  of 
air-spaces  an  internal  atmosphere,  which  is  in  communica- 
tion with  the  external  atmosphere  through  the  stomata. 
Hence,  water  vapor  is  constantly  passing  from  the  working 
cells  into  the  internal  atmosphere  and  diffusing  through  the 
stomata  into  the  external  atmosphere.  Although  a  certain 
amount  of  transpiration  takes  place  directly  through  the  epi- 
dermal cells,  much  the  larger  part  of  the  water  vapor  passes 
out  by  way  of  the  stomata.  If  the  stomata  are  closed  by  the 
guard-cells,  the  internal  atmosphere  becomes  saturated  with 
water  vapor  and  transpiration  ceases.  It  is  evident  that 
the  larger  the  air-spaces  in  the  leaf,  that  is,  the  looser  the 
leaf  is  in  texture,  the  greater  is  the  amount  of  internal 
atmosphere,  and  the  more  rapid  is  transpiration.  Hence 
the  amount  of  transpiration  from  a  leaf  depends  more  upon 
its  structure  than  upon  the  extent  of  its  exposed  surface. 

If  a  glass  vessel  (bell  jar)  be  placed  over  a  small  active 
plant,  the  moisture  is  seen  to  condense  on  the  glass,  and 
even  to  trickle  down  the  sides  (Eig.  17).*  When  the 

as  follows :  After  the  exposure  to  light,  the  leaves  were  placed  in  alcohol 
to  extract  the  green  coloring  matter  (chlorophyll).  When  this  was 
accomplished,  they  were  rinsed  thoroughly,  to  remove  the  alcohol,  and 
placed  in  a  water  solution  of  iodine.  In  this  solution  the  starch-con- 
taining portion  becomes  dark  blue,  the  other  portion  remaining  colorless. 
The  water  solution  of  iodine  is  obtained  by  dissolving  potassium  iodide 
in  water  and  adding  scales  of  iodine. 

*  Some  such  experiment  should  be  performed  to  demonstrate  the 
fact  of  transpiration.  Care  must  be  taken  to  shut  off  the  evaporation 
from  the  pot  or  soil,  since  it  is  to  be  demonstrated  that  water  is  coming 
from  the  plant.  Rubber  cloth  or  a  coating  of  paraffin  or  wax  may  be 
used  for  sealing  up  all  sources  of  moisture  except  the  plant  (Fig.  17). 


LEAVES 


23 


amount  of  water  given  off  by  a  few  leaves  is  noted,  some 
vague  idea  may  be  formed  as  to  the  amount  given  off  by  a 
great  mass  of  vegetation,  such  as  a  meadow  or  a  forest. 
One  observer  has 
stated  that  a  single 
stalk  of  corn  during 
its  life  (173  days) 
transpired  about  four 
gallons  of  water;  and 
that  a  single  hemp 
plant  (140  days) 
transpired  nearly 
eight  gallons.  An- 
other observer  esti- 
mated that  a  sun- 
flower, whose  leaf 
surface  was  approxi- 
mately nine  square 
yards,  gave  off  near- 
ly one  quart  of  wa- 
ter in  a  single  day. 

16.  Growth. —  In 
very  young  leaves 
growth  takes  place 

,  i        '     |  .       FIG.  17. — Transpiration  experiment:  a  potted  gera- 

at  the  apex,  but  tlllS          nium   sealed  with   a   rubber  cloth  and  covered 


with  a  bell  jar;   the  mist  and  droplets  of  water 
on  the  glass  more  or  less  obscure  the  plant. 


may  cease  early.  The 
subsequent  growth 
often  occurs  at  the  base  of  the  blade,  in  a  special  growing 
region,  as  may  be  seen  in  long  and  narrow  leaves  such  as 
those  of  grasses.  To  discover  these  special  regions  of 
growth  in  leaves,  some  rapidly  growing  plants  (such  as 
the  gourds)  should  be  cultivated  in  pots.  When  the 
young  leaves  first  appear,  a  scale  should  be  marked  off  in 
India  ink  with  a  pointed  camel's  hair  brush  on  the  petiole 

(if  there  be  one)  and  the  midrib.     The  scale  should  be  made 
3 


24  A  TEXT-BOOK  OF  BOTANY 

with  definitely  spaced  lines,  preferably  five  millimeters 
apart.*  As  the  leaf  continues  to  grow,  the  most  active 
growing  region  will  be  indicated  by  the  lines  that  draw 
farthest  apart. 

17.  Protection. — Such  an  important  organ  as  the  leaf, 
with  its  delicate  active  cells  necessarily  in  communication 
with  the  air,  is  exposed  to  numerous  dangers.  Conspicu- 
ous among  these  dangers  are  drought,  intense  light,  and 
cold.  Many  ways  of  meeting  these  dangers  have  been 
developed  by  plants,  but  the  subject  is  too  large  and  com- 
plex to  be  presented  with  any  completeness.  The  best 
that  can  be  done  is  to  select  a  few  striking  illustrations  of 
protection  that  seem  to  be  definite.  Perhaps  the  most 
common  danger  to  most  plants  is  an  excessive  loss  of  water, 
and  when  a  drought  prevails  the  problem  of  checking  trans- 
piration is  a  most  serious  one.  As  the  leaves  are  the 

prominent  transpiring  organs, 
the  chief  methods  of  protec- 
tion concern  them. 


A  B 

FIG.  18. — Sections  through  leaves  of  the  same  plant,  showing  the  effect  of  exposure 
to  light  upon  the  structure  of  the  mesophyll :  A,  leaf  exposed  to  intense  sun- 
light ;  B,  leaf  grown  in  the  shade. — After  STAHL. 

(1)  The  epidermis  may  be  regarded  as  an  ever-present 
check  against  transpiration   (Fig.  12),  for  without  it  the 

*  Such  scales  on  stem  and  root  are  seen  in  Figs.  57  and  75. 


LEAVES 


active  mesophyll  cells  would  soon  lose  all  their  water.  In 
some  plants  of  very  dry  regions,  what  may  be  regarded  as 
several  epidermal  layers  appear. 

(2)  The  palisade  layer  of  the  mesophyll  (§  13)  also  is 
very  commonly  present  and  tends  to  diminish  transpira- 


FIG.  19. — Section  througn  a  small  portion  of  yew  leaf,  showing  the  epidermal 
layer  (e)  with  its  cuticle  (c),  and  the  upper  portion  of  the  palisade  layer  (j>). 

tion,  exposing  only  the  ends  of  elongated  cells,  which  stand 
so  close  together  that  there  is  no  drying  air  between 
them  (Fig.  12).  It  is  very  characteristic  of  alpine  and 
desert  plants  to  form  two  or  three  layers  of  palisade  cells, 
apparently  as  a  protection 
against  unusual  danger  from 
drought  and  intensity  of 
light.  The  accompanying 
figure  (Fig.  18)  shows  in  a 
striking  way  the  effect  of 
light  intensity  upon  the 
structure  of  mesophyll,  by 
contrasting  leaves  of  the 
same  plant  exposed  to  ex- 
treme conditions  of  light 
and  shade.  Tne  intense 
light  is  dangerous  to  the 
chloroplasts,  and  it  has 


FIG.  20. — Section  through  a  small  portion 
of  carnation  leaf,  showing  the  epider- 
mal cells  (e)  with  their  heavy  cuticle 
(c);  a  single  stoma  in  the  epidermal 
layer,  opening  without  into  a  broad 
passageway  through  the  cuticle,  and 
within  into  an  air-chamber ;  and  the 
upper  portion  of  palisade  cells  (p)  con- 
taining chloroplasts. 


been  observed  that  they  are 
able  to  assume  various  positions,  in  very  intense  light  mov- 
ing to  the  more  shaded  depths  of  the  palisade  cells,  and  in  less 
intense  light  moving  to  the  more  external  regions  of  the  cell. 


A  TEXT-BOOK  OP  BOTANY 


FIG.  21. — Section  through  the  leaf  of  bush  clover, 
showing  upper  and  lower  epidermis,  palisade 
cells,  and  cells  of  the  spongy  tissue;  the  lower 
epidermis  produces  numerous  simple  hairs  that 
bend  sharply  and  lie  along  the  surface  of  the 
leaf. 


(3)  The   cuticle,   which   is   often   developed   upon   the 
epidermis,  is  one  of  the  best  protections  against  loss  of 
water.     It  is  developed  by  the  exposed  walls  of  the  epi- 
dermal cells,  and  being  constantly  renewed  from  beneath  it 
may  become  very  thick  and  many-layered  (Fig.  19).    Some- 
times the  cuticle  be- 
comes so  thick  that  the 
passageways  through 
it  to  the  stomata  re- 
semble tubes  (Fig.  20) . 
In  dry  regions,  or  in 
any    much     exposed 
place,  the  cuticle  is  a 
very  constant  feature 
of  plants. 

(4)  Hairs  in   great   variety   are   developed   upon   leaf 
surfaces,  being  outgrowths  from  the  epidermal  cells.     They 
may  form  only  a  slightly  downy  covering  (Fig.  21),  or  the 
leaf  may  be  covered  by  a  woolly 

or  felt-like  mass  so  that  the  epi- 
dermis is  entirely  concealed,  as 
in  the  common  mullein  (Fig.  22). 
In  dry  or  cold  regions  the  hairy 
covering  of  leaves  is  very  notice- 
able, often  giving  them  a  brilliant 
silky  white  or  bronze  look.  Some- 
times instead  of  hairs  the  epi- 
dermis develops  scales  of  various 
patterns  (Fig.  23),  often  overlap- 
ping and  forming  a  complete 
covering.  The  great  variety  of 
these  hairs  and  scales,  and  the 
ease  with  which  they  may  be  ex- 
amined, make  them  an  attractive  study.  At  the  same 
time,  just  how  they  protect  the  leaves  is  by  no  means 


FIG.  22. — Branching  hair  of 
mullein. 


LEAVES 


27 


clear;  and  doubtless  they  may  serve  other  purposes  also, 
or  sometimes  may  even  be  of  no  use  whatever  to  the 
plant.  It  has  been 
suggested  that  in  re- 
gions of  intense  light  a 
covering  of  hairs  is  an 
effective  sun  -  screen. 
The  explanation  is 
that  being  dead  struc- 
tures, containing  air, 
they  reflect  the  light, 
thus  diminishing  the 
amount  that  reaches 
the  working  cells.  As 
is  well  known,  hairs 
are  by  no  means  re- 
stricted to  leaves,  but 
occur  on  all  parts  of 
plants. 

(5)  Small  leaves  are 
characteristic    of    dry 

regions,  in  this  way  each  leaf  exposing  a  small  surface  to 
the  drying  air  and  intense  light.     That  this  reduction  in 

size  holds  a  direct  relation  to 
the  dry  conditions  is  evident 
from  the  fact  that  the  same 
plant  often  produces  small 
leaves  in  a  dry  region  and 
larger  ones  in  moist  condi- 
tions. In  the  case  of  the 
cactus,  a  large  group  in  the 
dry  regions  of  the  Southwest, 
the  leaves  have  become  so 
colorless  water  storage  tissue  <tc),  much  reduced  that  they  are 

and     the    central    cells    containing  . 

chioropiasts  (c).  no  longer  used  in  photosyn- 


FIG.  23. — Scale  from  the  leaf  of  Shepherdia ;  such 
scales  overlap  and  form  a  complete  covering. 


—  e 


28  A  TEXT-BOOK  OF  BOTANY 

thesis,  and  this  process  is  carried  on  by  the  green  tissue  of 
the  globular,  cylindrical,  or  flattened  stems  (Fig.  25). 


FIG.  25. — A  globular  cactus,  '.vith  ribbed  stem  bearing  spines  and  no  foliage  leaves. 

(6)  The  rosette-habit  (§  12)  is  a  very  common  method  of 
protection  used  by  small  plants  growing  in  exposed  situa- 
tions, as  bare  rocks  and  sandy  ground.  The  clustered 
leaves,  flat  upon  the  ground  or  nearly  so,  and  more  or  less 
overlapping,  form  a  very  effective  arrangement  for  resisting 
intense  light  or  drought  (Figs.  6  and  7). 


LEAVES  29 

(7)  Water  reservoirs  are  common  in  leaves  and  other 
parts  of  plants  of  dry  regions,  and  while  they  may  not  be 
regarded  as  a  protection  against  loss  of  water,  they  ac- 
complish the  same  purpose  in  storing  it.     Usually  the  water 
reservoir  is  a  definite  tissue,  and  in  many  leaves  it  may  bo 
distinguished   from   the   ordinary  green   working  cells   by 
being  a  group  of  colorless  cells  (Fig.  24).     In  plants  of  the 
drier  regions  leaves  may  become  thick  and  fleshy  through 
acting  as  water  reservoirs,  as  in  the  agave.     In  the  cactus 
the  peculiar  stems  have  become  great  reservoirs  of  moisture. 
The  globular  body  may  be  taken  to  represent  the  form  of 
body  by  which  the  least  amount  of  surface  may  be  exposed 
and  the  greatest  amount  of  water  storage  secured  (Fig.  25). 
In  the  case  of  these  fleshy  leaves  and  fleshy  bodies  it  has 
long  been  noticed  that  they  not  only  contain  water,  but  also 
have  great  power  of  retaining  it.     Plant  collectors  have 
found  much  difficulty  in  drying  these  fleshy  forms,  some  of 
which  seem  to  be  able  to  retain  their  moisture  indefinitely, 
even  in  the  driest  conditions. 

(8)  Profile  leaves   are   those   in   which   the   margin   is 
directed  upward,  in  this  way  standing  edgewise.     This  po- 
sition is  developed  in  connection  with  intense  light,  and 
results  in  turning  away  the  flat  faces  of  the  leaves  from  the 
intense  rays  of  midday  and  exposing  them  to  the  morning 
and  evening  rays  of  less  intensity.     In  the  dry  regions  of 
Australia  the  leaves  of  many  of  the  forest  trees  and  shrubs 
have  this  characteristic  edgewise  position,  giving  to  the 
foliage  a  peculiar  appearance.     The  most  famous  illustra- 
tion in  this  country  of  a  plant  with  profile  leaves  is  the  so- 
called  compass  plant,  a  rosin  weed  of  the  prairie  region. 
Its  name  was  given  because  its  leaves  were  said  to  point 
north  and  south,  serving  the  purpose  of  a  compass.     It  is 
evident  that  the  plane  of  a  profile  leaf,  exposing  its  faces  to 
the  morning  and  evening  sun,  will  lie  in  a  general  north 
and  south  direction.     It  is  a  significant  fact  that  when 


30 


A  TEXT-BOOK  OF  BOTANY 


i 


such  a  plant  grows  in  the  shade  the  leaves  do  not  assume 
the  profile  position.  It  must  not  be  supposed  that  there 
^  is  any  accuracy  in  the 

/    ^  -..,  /~~^  north  or  south  direction, 

)         as  the  edgewise  position 
is  the  significant  one.    In 
j£\    ^e   rosmweed    probably 
yjfia    the  north  and  south  di- 
9p      rection  is  the  prevailing 
f         one;  but  in  the   prickly 
^H     -?/f\          lettuce,  a  very  common 
weed  of  waste  grounds, 
and     one    of     the    most 
striking  of   the  compass 
plants,     the     edgewise 
position  is  frequently  as- 
sumed without  any  ref- 
erence  to    the   north   or 
south    direction    of    the 
apex  (Fig.  26). 

(9)  Motile  leaves  have 
the  power  of  shifting 
their  positions  according 
to  their  needs,  directing 
their  flat  surfaces  toward  the  light,  or  more  or  less  inclining 
them.  Such  leaves  have  been  developed  most  extensively 
in  the  great  family  to  which  peas  and  beans  belong,  the 
most  conspicuous  ones  being  those  of  the  so-called  sensitive 
plants.  The  name  has  been  given  because  the  leaves  respond 
to  various  external  influences  by  changing  position  with 
remarkable  rapidity.  A  slight  touch,  or  even  jarring,  will 
call  forth  a  response  from  the  leaves;  and  the  sudden  ap- 
plication of  heat  gives  striking  results  (Fig.  27).  The  most 
common  sensitive  plant  abounds  in  dry  regions,  and  may 
be  taken  as  a  type  of  such  plants.  The  leaves  are  divided 


FIG.  26. — Prickly  lettuce,  showing  the  edge- 
wise or  profile  leaves  from  two  points  of 
view. 


LEAVES 


31 


into  very  numerous  small  leaflets,  sometimes  very  small, 
which  stretch  in  pairs  along  the  leaf  branches.  When  a 
drought  begins,  some  pairs  of  leaflets  fold 
together,  slightly  reducing  the  surface  ex- 
posure. If  the  drought  continues,  more 


FIG.  27. — Leaf  of  sensitive  plant  in  two  conditions:  A,  fully  expanded,  with  the 
four  main  branches  and  numerous  leaflets  well  spread;  B,  after  a  shock  of  some 
kind,  the  leaflets  being  thrown  together  forward  and  upward,  the  four  branches 
having  been  moved  toward  each  other,  and  the  main  petiole  having  dropped 
sharply  downward. — After  DUCHARTRE. 

leaflets  fold   together,  then  still  others,  until   finally  all 
the  leaflets  may  be  folded  together,  and  the  leaves  them- 


A  B 

FIG.  28. — The  day  (A)  and  night  (B)  positions  of  the  leaves  of  a  clover-like  plant. 
— After  STRASBURGER. 

selves  may  bend  against  the  stem.     In  this  way  the  ex- 
posed surface  may  be  regulated  according  to  the  need. 


32 


A  TEXT-BOOK  OF  BOTANY 


Motile  leaves  also  shift  their  positions  throughout  the  day 
in  reference  to  light;  and  at  night  a  very  characteristic 
position  is  assumed,  once  called  a  sleeping  position,  but 
better  night  position.  The  contrast  between  the  day  and 
night  positions  of  leaves  such  as  those  of  the  sensitive  plants, 
and  even  of  the  common  white  clover,  is  quite  striking  (Fig. 
28).  These  night  positions,  produced  by  the  withdrawal 
of  light,  may  be  induced  by  placing  plants  in  darkness;  and 
experiments  will  show  that  the  power  is  more  common  than 
is  generally  supposed.  Just  what  it  means  is  not  clear. 
The  suggestion  has  been  made  that  the  night  position  is  a 
protection  against  danger  from  the  loss  of  heat,  but  it  may 
have  no  such  meaning. 

(10)  Rain  is  a  menace  to  leaves,  for  if  the  water  soaks 
in  and  fills  up  the  air  spaces  and  stomata,  communication 
with  the  air  is  cut  off;  hence  leaves  shed  water  with  remark- 
able promptness,  partly  by  their  positions,  partly  by  their 
structure.  Some  of  the  structures 
that  prevent  the  rain  from  soaking 
in  are  a  smooth  epidermis,  a  cuticle, 
a  waxy  deposit,  felt-like  coverings, 
overlapping  scales,  etc.  In  the 
rainy  tropics  it  is  very  common  for 

-..    mmsm  <?~&-^  the   sunken   veins   and  ribs  of  the 

r Fi  Hill/  leaves  to  form  a  sort  of   drainage 

system  for  carrying  off  water,  the 
main  channel  lying  along  the  midrib, 
which  terminates  in  a  long,  spout- 
like  point  (Fig.  319). 

18.  Fall  of  leaves. — Many  shrubs 
and  trees  of  temperate  regions  lose 
their  leaves  at  the  approach  of 
winter,  or  even  earlier,  putting  out 
new  leaves  in  the  following  spring.  This  is  called  the 
deciduous  habit,  and  it  is  an  adaptation  to  climate.  While 


FIG.  29.  —  Diagrammatic  sec- 
tion through  a  node  of  horse- 


(«)  and  the  vascular  bundle 
(6)  not  cut  through. 


LEAVES 


33 


in  some  deciduous  leaves,  as  those  of  oaks,  there  is  no 
special  preparation  for  falling,  in  most  of  them  a  special 
plate  of  cells  is  formed  at  or  near  the  juncture  of  the  leaf 
with  the  stem,  known  as  the  cutting-off  layer,  which  gradu- 
ally loosens  the  leaf  from  the  stem,  so  that  it  falls  by  its 
own  weight  or  is  wrenched  off  by  the  wind  (Fig.  29). 

In  connection  with  the  deciduous  habit  there  often 
appears  the  autumn  coloration  of  leaves,  so  striking  a  feat- 
ure of  temperate  forests. 
The  colors  that  appear 
are  shades  of  yellow  and 
red,  either  pure  or  vari- 
ously intermixed.  They 
are  the  result  of  the  wan- 
ing activity  of  the  leaf, 
the  yellow  mostly  being 
the  color  of  the  dying 
chloroplast,  and  the  red 
coming  from  the  pres- 
ence of  a  new  substance 
manufactured  in  the  en- 
feebled cells.  The  pop- 
ular belief  that  these 
colors  are  caused  by 
frost  is  only  partly  true, 
for  they  often  appear 
before  any  frost;  but 
they  may  be  induced 
by  any  conditions  that 
tend  to  diminish  the 
activity  of  the  leaf,  and 

Cold    is    One    Of    the   COn-  FlG    30._The  needle-]eaveS  of  a  pine. 

spicuous  conditions. 

19.  Leaves  of  evergreens. — In  contrast  with  the  decidu- 
ous shrubs  and  trees  are  the  so-called  evergreens,  in  which 


A  TEXT-BOOK  OF  BOTANY 


there  is  no  regular  annual  fall  of  leaves.  Such  leaves  en- 
dure for  a  varying  length  of  time;  but  as  there  is  no  regular 
period  for  all  of  them,  the  shrub  or  tree  always  appears  in 
foliage.  In  the  temperate  regions  the  most  conspicuous 

evergreens  are  the  pines  and 
their  allies.  A  comparison 
between  the  needle-leaf  of  a 
pine  and  the  leaf  of  an  ordi- 
nary deciduous  tree  will  show 
what  the  evergreen  habit  in- 
volves in  temperate  regions 
(Fig.  30).  The  leaf  of  a  pine 
must  be  protected  so  as  to 
endure  the  winter,  and  this 
has  involved  reduction  of 
surface  and  extremely  thick 
protective  layers  about  the 
mesophyll  (Fig.  31).  This, 
has  diminished  the  ability  to 
work;  but  it  has  saved  the 

tree  the  necessity  of  putting  out  a  complete  new  crop  of 
leaves  for  the  next  season.  The  deciduous  leaf,  on  the 
other  hand,  is  broad  and  thin,  with  great  capacity  for 
work;  but  this  forbids  protection  during  the  winter. 

20.  Special  forms  of  leaves. — Besides  the  ordinary  leaves 
that  have  been  considered,  and  which  are  called  in  distinc- 
tion foliage  leaves,  there  are  special  forms  of  leaves  whose 
chief  work  is  different.  In  so  far  as  they  are  green,  they 
manufacture  carbohydrates  as  do  the  foliage  leaves,  but  a 
distinct  change  in  structure  and  behavior  indicates  that  this 
is  not  their  chief  work. 

(1)  Scales. — The  most  conspicuous  illustrations  of 
leaves  that  have  become  modified  into  scales  are  to  be  found 
in  subterranean  stems  and  scaly  buds.  Underground  stems 
cannot  produce  foliage  leaves  on  account  of  the  absence  of 


m 


FIG.  31. — Cross-section  of  the  needle- 
leaf  of  a  pine,  showing  the  epider- 
mis with  heavy  cuticle  (e),  in  which 
are  sunken  stomata  (s);  masses  of 
heavy-walled  cells  (h)  beneath  the 
epidermis;  the  mesophyll  region  (m) 
containing  chloroplasts,  and  the  cen- 
tral colorless  region  containing  two 
vascular  bundles. — After  SACHS. 


LEAVES 


35 


light,  but  they  produce  leaves  reduced  in  size  and  without 
green  tissue.  Often  these  scales  seem  to  be  merely  useless 
relics  (Fig.  64);  but  sometimes  they  are  used  for  food 
storage,  as  in  lily  bulbs,  onions,  etc.,  which  are  mostly  made 
up  of  fleshy  scales  (Fig.  65). 

In  the  scaly  buds,  so  common  on  shrubs  and  trees,  the 
overlapping  scales  are  clearly  protective  structures,  and  to 
this  end  are  generally  firm  and  resistant,  often  coated  with 
resin,  the  inner  ones  being  frequently  clothed  with  woolly 
hairs. 

(2)  Tendrils. — The  whole  leaf  or  some  of  its  branches 
may  develop  as  tendrils,  the  latter  case  being  illustrated  by 
the  sweet  pea   (Fig.   32).     Ten- 
drils   are    sensitive     to    contact 

and  aid  in  climbing.  Some- 
times  leaves  act  as  tendrils 
without  any  modification  of  the 
blade,  the  petiole  being  sensitive 
to  contact  and  encircling  sup- 
ports like  a  tendril,  as  in  the 
irarden  nasturtium. 

(3)  Thorns. — Leaves  develop- 
ing as  thorns  may  be  observed 
in  the  barberry  (Fig.  33).    In  the 
•common  locust,  acacia,  etc.,  only 
the  stipules  develop  as  thorns. 

Both  tendrils  and  thorns  are 
also  developed  as  stem  struc- 
tures, being  modified  branches. 

(4)  Leaves  of  pitcher-plants. — 
In  these  plants  the  leaves  form 
tubes  or  urns  of  various  forms, 
which  contain  water;  and  to  these 

insects  are  attracted  and  drowned.  The  common  pitcher- 
plant  of  the  northern  States,  a  Sarracenia,  is  a  well-known 


FIG.  32. — Pinnately  compound 
leaf  of  garden  pea,  whose  ter- 
minal portion  has  developed 
as  tendrils.  —  After  STRAS- 

BURGER. 


36 


A  TEXT-BOOK  OF  BOTANY 


bog  plant  (Fig.  34),  but  is  not  so  elaborately  constructed 
for  capturing  insects  as  is  a  common  southern  Sarra- 
cenia  (Fig.  35).  In  this  plant  the  leaves  are  slender,  hol- 
low cones,  and  rise  in  a  tuft  from  the  swampy  ground. 
The  mouth  of  this  conical  urn  is  overarched  and  shaded  by 
a  hood,  in  which  are  translucent  spots,  like  numerous  small 
windows.  Around  the  mouth  of  the  urn  are  glands  which 

secrete  a  sweet  liq- 
p  uid,  known  as  nectar. 
Inside,  just  below 
the  rim  of  the  urn, 
is  a  glazed  zone,  so 
smooth  that  insects 
cannot  walk  upon 
it.  Below  the  glazed 
zone  is  another  one 
thickly  set  with  stiff, 
downward-pointing 
hairs;  and  below  this 
is  the  liquid  in  the 
bottom  of  the  urn. 
If  a  fly,  attracted  to 
the  nectar  at  the  rim 
of  the  urn,  attempts 
to  descend  within  the 
urn,  it  slips  on  the 
glazed  zone  and  falls 
into  the  water;  and 
if  it  attempts  to 
escape  by  crawling, 
the  downward-point- 

FIG.  33. — Leaves  of  barberry  developing  as  thorns. 

ing  hairs  prevent.     If 

it  seeks  to  fly  from  the  rim,  it  naturally  flies  toward  the 
translucent  spots  in  the  hood,  since  the  direction  of  en- 
trance is  in  the  shadow;  and  pounding  against  the  hood, 


LEAVES 


37 


the  fly  usually  falls  into  the  tube.  The  pitchers  gen- 
erally contain  the  decaying  bodies  of  numerous  drowned 
insects. 

A  much  larger  Californian  pitcher-plant  is  Darlingtonia 
(Fig.  36),  whose  leaves  are  one  and  a  half  to  three  feet 
high,  the  hood  bearing  a 
gaudily  colored  "  fish-tail " 
appendage,  the  whole  struc- 
ture being  a  more  elaborate 


FIG.  34. — Leaves  of  the  common 
northern  pitcher -plant,  one  of 
them  sectioned  to  show  cavity 
and  wing. — After  GRAY. 


FIG.  35. — Leaf  of  a  southern  pitcher-plant, 
showing  the  funnelform  and  winged 
pitcher,  and  the  overarching  hood  with 
translucent  spots. — After  KKKNKK. 


insect  trap  than  are  the  leaves  of  Sarracenia.  In  these 
traps  not  only  are  the  remains  of  flies  found,  but  bees, 
hornets,  butterflies,  beetles,  grasshoppers,  and  even  snails 
have  been  reported. 


38 


A  TEXT-BOOK  OF  BOTANY 


The  species  of  Nepenthes  from  the  oriental  tropics,  very 
common  in  conservatories,  develop  most  remarkable  leaves, 

the  lowest  part  being  an  ordi- 
nary blade,  beyond  which  is  a 
well-developed  tendril,  at  the 
end  of  which  there  arises  an 


FIG.  36. — Leaves  of  the  Californian  pitcher- 
plant,  showing  the  twisted  and  winged 
pitcher,  the  overarching  hood  with  trans- 
lucent spots,  and  the  fish-tail  appendage 
to  the  hood. — After  KEENER. 


FIG.  37. — Leaf  of  Nepenthes,  show- 
ing the  blade-like  base,  the  ten- 
dril portion,  and  the  terminal 
pitcher  with  its  lid.  —  After 
GRAY. 


elaborate  pitcher  with  a  lid  (Fig.  37).  There  is  the  same 
sweetish  secretion  at  the  rim  of  the  pitcher,  and  the  same 
accumulation  of  water  within  as  in  the  ordinary  pitcher- 
plants. 

(5)    Leaves   of   sundews. — The    sundews   are    forms    of 
Drosera  and  grow  in  swampy  regions,  the  leaves   forming 


LEAVES 


39 


small  rosettes  upon  the 
ground  (Fig.  38),  In  one 
form  the  blade  is  round, 
and  the  margin  is  beset 
by  prominent  bristle-like 
hairs,  each  with  a  globu- 
lar gland  at  its  tip  (Fig. 
39).  Shorter  gland-bear- 
ing hairs  are  scattered  also 
ever  the  inner  surface  of 
the  blade.  All  these  glands 
excrete  a  clear,  sticky  fluid, 
which  hangs  to  them  like 
dewdrops,  and  which,  not  _, 
being  dissipated  by  sun- 
light,  has  suggested  the 
name  sundew.  If  a  small 
insect  becomes  entangled  in 


FIG.  38. — Sundews. — After  KERNER. 


FIG.  39. — Two  leaves  of  a  sundew:     A,  glandular  hairs  fully  extended;  B,  half 
the  hairs  bending  inward,  in  the  position  assumed  when  an  insect  has  been 
captured. — After  KERNER. 
4 


40 


A   TEXT-BOOK  OF  BOTANY 


one  of  the  sticky  drops,  the  hair  begins  to  curve  inward,  and 
presently  presses  its  victim  down  upon  the  surface  of  the 
blade.  In  the  case  of  a  larger  insect,  several  of  the  mar- 
ginal hairs  may  join  to- 
gether in  holding  it,  or  the 
whole  blade  may  become 
more  or  less  rolled  inward. 
(6)  Leaves  of  Dioncea. 
— This  is  one  of  the  most 
famous  and  remarkable  of 
insect-trapping  plants,  be- 
ing found  only  in  certain 
sandy  swamps  near  Wil- 
mington, N.  C.  The  leaf- 
blade  is  constructed  so  as 
to  work  like  a  steel  trap, 
the  two  halves  snapping 
together,  and  the  marginal 
bristles  interlocking  like 
the  teeth  of  a  trap  (Fig. 

FIG.  40.— Three  leaves  of  Dioncea:  two  with      40).      A  few  Sensitive  hairs, 
the  traps  open,  one  with  trap  shut  on      TI        r      i  i          i 

aninsect.-AfterKERNER.  ^k^  feelers,  are  developed 

on  the  leaf  surface ;    and 

when  one  of  these  is  touched  by  a  small  flying  or  hover- 
ing insect,  the  trap  snaps  shut  and  the  insect  is  caught. 
Only  after  digestion,  which  is  a  slow  process,  does  the  trap 
open  again.  Dioncea  is  popularly  known  as  the  "Venus 
fly-trap." 

Sarracenia,  Drosera,  and  Dioncea  are  conspicuous  repre- 
sentatives of  the  so-called  carnivorous  or  insectivorous 
plants,  all  of  which  capture  insects  and  use  them  for  food. 
They  are  green  plants,  so  that  they  manufacture  carbo- 
hydrates; but  for  some  reason  they  supplement  their  food 
manufacture  with  a  supply  of  food  already  manufactured, 
and  obtained  from  the  bodies  of  captured  insects. 


CHAPTER  III 

STEMS 

21.  Relation  to  other  organs. — The  stem  is  connected 
with  the  roots  and  bears  the  leaves.     So  constant  a  feature 
of  the  stem  is  leaf-bearing  that  the  presence  of  leaves  is  one 
method  of  distinguishing  underground  stems  from  roots. 
Not  merely  do  stems  bear  leaves,  but  they  usually  bear 
them  in  such  a  way  as  to  expose  them  well  to  the  air  and 
the  sunlight.     Often  stems  branch,  and  in  this  way  in- 
crease their  power  of  producing  and  displaying  leaves.     It 
is  evident  that  the  stem,  more  than  anything  else,  is  the 
leaf-bearing  organ;  and  in  bearing  leaves  it  must  be  also 
the  channel  of  communication  between  them  and  the  roots. 

So  closely  associated  are  stems  and  leaves  that  they  are 
spoken  of  together  as  the  shoot;  and  thus  the  whole  body  of 
the  plant  of  ordinary  experience  is  said  to  consist  of  shoot 
and  root,  the  former  usually  exposed  to  the  air  (aerial), 
the  latter  usually  exposed  to  the  soil  (subterranean).  As 
any  branch  is  merely  a  repetition  of  the  stem  from  which  it 
arises,  so  any  branch  with  its  leaves  is  a  shoot,  just  as  the 
whole  stem  system  with  its  leaves  is  a  shoot. 

22.  External  structure. — The  ordinary  stem  is  a  jointed 
structure.     While  this  is  very  evident  in  such  stems  as  the 
corn-stalk  and  the  cane  (seen  in   fishing-rods),  it  is  often 
made  apparent  only  by  the  leaves,  which  appear  at  the 
joints  or  nodes  (§  8).     The  portions  of  the  stem  between  the 
nodes — portions  which  do  not  bear  leaves — are  the  internodes; 
hence  a  stem  is  a  series  of  alternating  nodes  and  internodes. 

41 


A  TEXT-BOOK  OF  BOTANY 


FIG.  41.—  A  scarlet  runner  bean,  showing  leaf- 

ilternodes'  and 


Branches  as  well  as  leaves  appear  at  the  nodes;  and  there  is 
usually  a  very  definite  relation  between  them,  the  branch 

appearing  in  the  up- 
per angle  between  leaf 
and  stem,  called  the 
axil  of  the  leaf  (Fig. 
41).  Most  branches 
are  thus  axillary  in 
position.  The  inter- 
nodes  give  length  to 
the  stem,  separating 
the  nodes  from  each 
other,  and  so  display- 

ing     the     leaves     more 

freely  to  the  air  and 
the  sunlight. 

23.  Direction  of  stems.  —  The  directions  in  which  stems 
grow  are  due  to  a  variety  of  causes,  some  of  which  will  be 
considered  later;  but  for  the  present  only  certain  positions 
will  be  noted. 

(1)  Erect  stems.  —  The  upright  stem  is  the  most  common; 
and  it  seems  altogether  the  best  adapted  for  the  proper 
display  of  leaves,  for  they  can  be  spread  out  on  all  sides 
and  carried  upward  toward  the  light.  To  maintain  the 
erect  position  is  not  a  simple  mechanical  problem,  and  in 
large  woody  stems  it  involves  an  extensive  development 
and  arrangement  of  supporting  tissues.  That  some  special 
organization  is  necessary  to  maintain  the  erect  position  in 
the  air  is  evident  when  aerial  erect  stems  are  contrasted 
with  submerged  erect  stems.  In  small  lakes  and  slow- 
moving  streams  submerged  plants  are  commonly  seen,  as 
the  pickerel-weed  and  numerous  others.  In  the  water 
the  stems  are  erect;  but  when  taken  out  they  collapse, 
having  been  sustained  in  position  by  the  water. 

Among  aerial  seems  the  tree  is  the  most  impressive,  and 


STEMS 


it  has  developed  into  a  great  variety  of  forms  or  habits. 
In  some  trees,  as  the  pines  and  their  allies,  the  main  stem 
continues  as  a  central  shaft  to  the  top,  the  branches  spread- 


' 


42. — An  Austrian  j>ine. 


ing  horizontally  from  it  (Fig.  42);  while  in  other  trees,  as 
the  oak  and  the  elm  (Figs.  43  and  44),  the  main  stem 
soon  divides  into  large  branches.  In  the  former  case  the 


44  A   TEXT-BOOK  OF  BOTANY 

tree  has  a  general  conical  outline;  in  the  latter  case  it  has  a 
spreading  top  or  crown.     It  is  an  excellent  plan  to  become 


FIG.  43. — An. oak  in  winter  condition. 


acquainted  with  the  common  trees  of  a  neighborhood  and 
to  learn  to  recognize  them  by  their  habits.  Trees  are  also 
an  excellent  illustration  of  the  fact  that  while  the  main 
stem  of  a  plant  may  be  erect,  the  branches  may  be  di- 


STEMS 


45 


reeled  at  any  angle,  often  horizontal,  and  sometimes  even 
descending. 

(2)  Prostrate  stems. — In  many  plants  the  main  stem  or 
certain  branches  lie  prostrate  on  the  ground  or  nearly  so, 


Fn;.  44. — An  elm  in  f ullage. 


sometimes  spreading  in  all  directions  and  becoming  inter- 
woven into  a  mat  or  carpet   (Fig.  45).     They  are  found 


46  A  TEXT-BOOK  OF  BOTANY 

especially  on  sterile  and  exposed  soil,  and  there  may  be  an 
important  relation  between  this  fact  and  their  habit.  In 
such  stems  there  is  a  distinct  disadvantage  in  the  display 


FIG.  45.— Prostrate  stem  of  Potentilla. 


of  leaves  as  compared  with  erect  stems;  for  instead  of  being 
free  to  spread  out  leaves  on  all  sides,  one  side  is  against  the 
ground,  and  the  free  space  for  them  is  diminished  at  least 
one-half.  All  the  leaves  such  a  stem 
bears  are  necessarily  directed  toward 
the  free  side. 


FIG.  46. — A  strawberry-plant,  showing  a  runner  that  has 
developed  a  new  plant,  which  in  turn  has  sent  out  an- 
other runner. — After  SEUBERT. 


We  may  not  know  all  the  reasons  why  so  unfavorable  a 
position  for  leaf  display  is  assumed ;  but  among  the  results 
are  protection  in  exposed  situations  in  some  cases,  and  the 


STEMS 


47 


multiplication  of  plants  in  others.  In  many  plants,  as  the 
prostrate  stem  advances  over  the  ground,  roots  develop  from 
the  nodes  and  enter  the  soil,  leaves  are  formed,  and  a  new 
plant  is  started,  which  may  become  independent  by  the 
death  of  the  older  parts.  In  this  way  a  plant  may  spread 
over  the  ground,  multiplying  itself  indefinitely.  So 
effective  is  this  method  of  multiplication  that  plants  with 
erect  stems  often  make  use  of  it,  sending  out  from  near  the 
base  special  prostrate  branches  which  advance  over  the 
ground  and  start  new  plants.  A  very 
familiar  illustration  is  furnished  by  the 
strawberry-plant,  which  sends  out  peculiar 
leafless  runners  to  strike  root  at  the  tip  and 
start  new  plants,  which  become  independent 
by  the  death  of  the  runners  (Fig.  46). 

These  various  prostrate  stems  illustrate 
the  fact  that  nodes  can  produce  not  only 
leaves  and  branches,  but  also  roots,  if 
placed  in  suitable  conditions.  Advantage 
is  taken  of  this  fact  in  the  common  process 
of  layering,  in  which  such  stems  as  those 
of  blackberries  and  raspberries  are  bent 
down  to  the  ground  and  covered  with  soil, 
when  the  nodes  strike  root  and  new  plants 
are  started. 

(3)  Climbing  stems. — A  great  many 
plants  have  developed  the  ability  to  sus- 
tain themselves  by  using  supports.  Al- 
though not  able  to  stand  alone,  by  using 
these  supports  they  may  attain  great  length 
and  display  their  leaves  to  light  even  in  a 
dense  forest.  This  climbing  is  effected  in 
a  variety  of  ways.  In  some  cases,  as  the  morning-glory, 
bean,  and  hop-vine,  the  stem  twines  about  the  support, 
such  plants  often  being  distinguished  as  twiners  (Fig.  47); 


bean 


twining   about 
support. 


A   TEXT-BOOK  OF   BOTANY 


in  other  cases,  as  the  grape-vine  and  star-cucumber,  tendrils 
are  formed,  which  twine  or  hook  about  the  supports  (Fig. 
48) ;  in  still  other  cases,  as  the  woodbine,  the  tendrils  pro- 
duce suckers  that  act  as 
holdfasts  and  enable  the 
plant  to  cling  to  trees  or 
walls  (Figs.  49  and  50). 
It  is  in  the  dense  forests 
of  the  tropics  that  climb- 
ing plants  become  espe- 
cially conspicuous.  There 
great  woody  vines  fairly 
interlace  the  vegetation, 
and  are  known  as  lianas 
or  lianes. 

If  a  young  morning- 
glory  or  twining  bean  be 
watched,  it  will  be  dis- 

FIG.  48.-Branch  of  star-cucumber,  with  its     covered    that    the    elonga- 
tendrils  in  various  conditions. 

ting   stem    is    unable    to 

stand  upright,  and  that,  as  it  bends  over,  the  inclined  part 
begins  to  swing  through  a  horizontal  curve,  which  may  bring 
the  stem  in  contact  with  a  suitable  support.  If  this  hap- 
pens, the  stem,  continuing  to  swing  in  a  curve  and  growing 
in  length  at  the  same  time,  winds  itself  about  the  support. 
This  movement  of  the  portion  of  the  stem  which  is  in  a  hori- 
zontal position  is  thought  to  be  brought  about  by  a  peculiar 
response  of  the  plant  to  gravity.  The  influence  of  gravity 
in  directing  plant  organs  will  be  considered  later. 

Tendrils  are  illustrations  of  plant  structures  that  are 
unusually  sensitive  to  contact.  When  the  tip  of  a  tendril 
in  moving  about  touches  a  suitable  support,  the  side  touched 
becomes  concave  and  the  tendril  hooks  or  coils  about  the 
support.  This  is  only  the  first  response  of  the  tendril  to 
contact,  for  presently  the  rest  of  it  begins  to  curve — a  move- 


STEMS 


1  i<;.  49. — Woodbine  in  a  deciduous  forest. 

ment  which  results  in  spiral  coils,  since 
the  tendril  is  fastened  at  both  ends  (Fig. 
48).  This  curving  and  twist- 
ing of  the  tendril  between  its 
fastened  extremities  naturally 
results  in  two  spiral  coils  run- 
ning in  opposite  directions.  In 
this  way  the  stem  is  fastened 
to  its  support  by  numerous 
spiral  springs.  All  of  these 
movements  and  their  results 
may  be  observed  by  cultiva- 
ting a  plant  such  as  the  star- 
cucumber,  which  growls  rapidly 
and  has  conspicuous  and  very 
sensitive  tendrils.  In  the  case 
of  the  ordinary  climbing  wood- 
bine and  certain  species  of  ivy, 

J  '     FIG.  50. — Woodbine  clinging  to  a  wall 
Which     cling     tO    Walls    Or     tree       .     by  means  of  tendril  suckers. 


50 


A  TEXT-BOOK  OF  BOTANY 


trunks,  the  tip  of  the  tendril  when  it  comes  into  contact 
with  a  support  is  stimulated  into  developing  the  sucker- 
like  disk  which  acts  as  a  holdfast  (Fig.  50). 
* —  24.  Internal  structure. — As  the  stems  of  seed-plants 
show  two  distinct  types  of  structure,  it  will  be  necessary  to 
point  out  the  great  groups  of  seed-plants,  so  that  the  types 
of  structure  may  be  referred  to  them.  The  Gymnosperms 
include  the  pines  and  their  allies,  the  common  evergreens; 
the  Monocotyledons  include  such  plants  as  grasses,  lilies, 
and  palms;  the  Dicotyledons,  much  the  largest  group, 
include  the  common  deciduous  trees,  such  as  oak,  maple, 
hickory,  poplar,  beech,  etc.,  as  well  as  the  great  majority 
of  common  herbs.  In  stem  structure  the  Gymnosperms. 
and  the  Dicotyledons  show  the  same  general  plan,  while 
the  other  type  of  structure  is  exhibited  by  the  Monocotyle- 
dons. 

(1)  Gymnosperms  and  Dicotyledons. — If  an  active  twig 
of  an  ordinary  woody  plant  be  cut  across,  it  will  be  seen 

that  it  is  made  up  of  four 
general    regions   (Fig.   51): 
~.     W  an  outer  Protecting  lay- 
er which  may  be  stripped 
'P  off  as  a  thin  skin,  the  epi- 
•c  dermis;    (2)    within   this  a 
zone  of  spongy  tissue,  usu- 
ally green,  the   cortex;    (3) 
then  a  relatively  broad  zone 
of  firm  wood,  the  vascular 
cylinder;  and  (4)  in  the  cen- 
ter the   pith.     The  special 
feature  of  this  arrangement 
is  that  the  wood  occurs  as 

a  hollow  cylinder,  enclosing  the  pith  and  surrounded  by 
the  cortex.  In  the  older  parts  of  stems  the  pith  often  dis- 
appears, leaving  a  hollow  stem.  The  cortex  is  the  active. 


W 


FIG.  51. — Cross-section  of  a  branch  of  box 
elder  one  year  old  :  e,  epidermis  ;  c, 
cortex ;  w,  vascular  cylinder ;  p,  pith. 


STEMS 


51 


working  region  of  the  stem:  since  it  is  green  it  is  able  to 
manufacture  carbohydrates  as  do  the  leaves  (§  14);  and  it 
is  also  concerned  in  other  work  connected  with  nutri- 
tion. The  vascular  cylinder,  on  the  other  hand,  is  the 
great  conducting  region,  as  well  as  one  that  gives  rigidity 
to  the  stem.  This  work  of  conduction  will  be  considered 
later. 

If  the  vascular  cylinder  be  examined  closely,  it  will  be 
seen  that  it  is  broken  up  into  segments  by  plates  of  cells 
that  traverse  it  from  the  pith  to  the  cortex,  these  radiating 
plates  of  cells  being  the  pith  rays  (Fig.  51).  The  cylinder  is 
thus  made  up  of  a  number  of  segments  which  are  called 
vascular  bundles.  The  peculiarity  of  the  structure  of  the 
stem  in  Gymnosperms  and  Dicotyledons,  therefore,  can  be 
described  as  the  arrangement  of  the  vascular  bundles  so  as 


FIG.  52. — Cross-section  of  vascular  bundle  from  pine  stem,  showing  xylem  (i), 
cambium  (c),  and  phloem  (p)  ;  on  each  side  of  the  single  row  of  cambium 
cells  there  are  young  xylem  and  phloem  cells  that  pass  gradually  into  the 
mature  condition. 

to  form  a  hollow  cylinder.  In  woody  stems  the  bundles 
are  very  close  together  in  the  cylinder,  forming  a  compact 
cylinder  with  narrow  pith  rays;  but  in  the  stems  of  herbs 
the  bundles  are  well  separated,  leaving  broad  pith  rays. 

If  the  cross-section  of  an  individual  vascular  bundle  be 
examined  under  the  microscope,  two  regions  will  be 
recognized  (Fig.  52) :  the  inner  one,  toward  the  pith,  being 
called  wood  (xylem),  and  the  outer  one  being  called  bast 


52 


A   TEXT-BOOK   OF  BOTANY 


(phloem)*  A  vascular  bundle,  therefore,  is  made  up  of 
wood  and  bast,  which  differ  from  one  another  in  the  work 
of  conduction,  the  wood  chiefly  conducting  the  water  that 
enters  the  plants  by  the  roots  and  is  passing  to  the  leaves, 
and  the  bast  chiefly  conducting  prepared  food. 

The  cells  of  the  wood  that  conduct  water  are  called 
tracheary  vessels.  They  are  more  or  less  elongated  and 
have  very  thick  walls,  upon  which  there  appear  markings 
of  various  kinds.  These  markings  may  be  seen  in  a 


B 


FIG.  53. — Vessels :  spiral  (A)  and  annular  (5)  vessels ;  dotted  vessel  (C)  ;  sieve 
vessel  (D)  and  sieve  plate  (E)  from  pumpkin. — A  and  B  after  BONNIER  and 
SABLON  ;  C  after  DE  BARY  ;  D  after  STRASBURGER. 

longitudinal  section  through  the  wood.  Some  of  the  vessels 
are  marked  by  a  spiral  band  that  extends  from  end  to  end, 
and  are  called  spiral  vessels  (Fig.  53,  A);  others  show  a 
series  of  thickened  rings,  and  are  called  annular  vessels 
(Fig.  53,  B);  while  others,  and  among  them  the  largest, 

*  If  a  cross-section  of  a  pine  twig  be  stained  first  with  safranin  and 
afterward  with  Delafield's  haematoxylon,  the  xylem  will  become  bright 
red  and  the  phloem  rich  violet. 


STEMS  53 

have  numerous  thin  spots  in  their  walls  which  look  like 
dots  of  various  sizes,  and  these  are  the  dotted  or  pitted 
vessels  (Fig.  53,  C),  often  called  dotted  ducts.  These  pitted 
vessels  are  often  very  large,  their  openings  being  visible  to 
the  naked  eye  in  the  cross-section  of  oak  wood. 

The  cells  of  the  bast  that  conduct  prepared  food  are 
called  sieve  vessels  (Fig.  53,  D),  because  in  their  walls, 
usually  the  end  walls,  there  appear  areas  full  of  perfora- 
tions, like  the  lid  of  a  pepper-box,  these  areas  being  called 
sieve-plates  (Fig.  53,  E). 

The  veins  of  leaves  are  vascular  bundles  that  are 
continuous  with  those  of  the  stem.  If  the  relative  positions 
of  wood  and  bast  in  the  stem  be  remembered,  it  will  be 
seen  that  when  a  bundle  turns  out  into  a  leaf,  the  wood 
with  its  tracheary  vessels  is  toward  the  upper  side  of  the 
leaf,  and  the  bast  with  its  sieve  vessels  toward  the  lower 
side. 

A  prominent  feature  of  such  stems  is  that  they  can 
increase  in  diameter.  If  the  stem  lasts  only  one  growing 
season,  that  is,  if  it  is  an  annual,  the  increase  in  diameter 
does  not  occur;  but  if  it  lasts  through  several  seasons,  that 
is,  if  it  is  a  perennial,  it  increases  in  diameter  from  year  to 
year.  Naturally  annual  stems  belong  to  herbs  and  perennial 
stems  to  shrubs  and  trees.  Taking  the  tree  as  an  illustra- 
tion, the  increase  in  diameter  occurs  as  follows:  Between 
the  wood  and  the  bast  of  each  bundle  is  a  layer  of  very 
active  cells  called  the  cambium  (Fig.  52,  c),  which  soon 
extends  across  the  intervening  pith  rays,  and  so  forms  a 
complete  cylinder  of  cambium.  This  cambium  has  the 
power  of  adding  new  wood  cells  to  the  outer  surface  of  the 
wood,  and  new  bast  cells  to  the  inner  surface  of  the  bast, 
as  well  as  adding  to  the  pith  rays  where  it  traverses  them. 
In  this  way  a  new  layer  of  wood  is  laid  down  on  the  outside 
of  the  old  wood;  and  usually  these  layers,  added  year  after 
year,  are  so  distinct  that  a  section  of  wood  shows  a  series 


A  TEXT-BOOK  OB"  BOTANY 


of  concentric  rings  (Fig.  54).  Ordinarily  one  such  layer  is 
added  each  year,  and  hence  the  layers  are  called  annual 
rings.  The  age  of  a  tree  is  usually  estimated  by  counting 

these  rings,  but  occasion- 
ally more  than  one  ring 
may  be  added  during  a 
single  year.  The  new 
layers  added  to  the  bast 
are  not  persistent;  but 
the  wood  accumulates 
year  after  year,  until  in 
an  ordinary  tree  the 
stem  is  a  great  mass  of 
wood  covered  with  thin 
layers  of  bast  and  cor- 
tex. It  is  this  mass  of 
wood  that  supplies  our 
lumber. 

This  annual  increase 
in  diameter  enables  the 
tree  to  put  out  an  in- 
creased number  of  branches,  and  hence  leaves,  each  suc- 
ceeding year,  so  that  its  capacity  for  leaf  work  becomes 
greater  year  after  year.  A  reason  for  this  is  that  since  the 
wood  is  conducting  water  to  the  leaves,  for  food  manufac- 
ture, the  new  layers  enable  it  to  conduct  more  water,  and 
more  leaves  can  be  supplied. 

When  a  stem  increases  in  diameter  it  is  very  seldom 
that  the  epidermis  grows  in  proportion.  Hence  it  is  usu- 
ally sloughed  off  and  a  new  protective  covering  is  de- 
veloped by  the  cortex.  Either  the  outermost  layer  of  the 
cortex  or  some  deeper  one  becomes  a  cambium,  which 
means  that  it  is  able  to  form  new  cells.  This  cambium  is 
called  the  cork  cambium,  since  it  forms  at  its  outer  surface 
layer  after  layer  of  cork  cells,  which  are  peculiarly  resistant 


FIG.  54. — Cross-section  of  a  branch  of  box 
elder  three  years  old,  showing  three  an- 
nual rings  in  the  vascular  cylinder;  the 
radiating  lines  (TO)  which  cross  the  vascu- 
lar ring  (w;)  represent  the  pith  rays,  the 
principal  ones  extending  from  pith  to  cor- 
tex (c). 


STEMS  55 

to  water.  If  the  cork  cambium  is  formed  deep  in  the  cortex, 
all  the  cells  outside  of  it  die,  since  they  are  cut  off  from  the 
water  supply  in  the  plant.  The  cork  cambium  is  often 
renewed  year  after  year,  and  two  prominent  kinds  of  bark 
are  formed.  In  some  cases  the  successive  cork  cambiums 
form  zones  completely  about  the  stem,  and  the  cork  is  then 
deposited  in  concentric  layers,  forming  the  ringed  bark. 
Such  bark  often  becomes  very  thick,  and  the  surface 
becomes  seamed  or  furrowed.  In  the  cork  oak  there  is  a 
very  great  accumulation  of  cork,  which  is  stripped  off  in 
sheets,  from  which  corks  of  commerce  are  made.  In  other 
cases  the  successive  cork  cambiums,  instead  of  passing 
completely  around  the  stem,  run  into  the  next  outer  one, 
thus  cutting  out  segments  which  presently  loosen  and  flake 
off,  forming  scaly  bark,  as  in  hickory,  apple,  etc. 

The  layers  of  cork  and  other  cells  that  may  lie  outside 
of  the  cork  cambium  form  the  outer  bark,  which  is  dead 
and  dry.  The  tissues  between  the  cork  cambium  and  the 
cambium  of  the  vascular  cylinder,  that  is  more  or  less 
cortex  and  the  bast,  form  the  inner  bark,  which  contains 
some  living  cells.  To  remove  the  outer  bark  does  not  injure 
a  tree;  but  removing  the  inner  bark  kills  it,  because  it 
interrupts  the  work  of  conduction  carried  on  by  the  sieve 
vessels.  In  the  process  known  as  girdling,  not  only  is  the 
bark  cut  through,  but  the  young  wood  is  cut  into.  This 
interferes  with  the  movement  of  water  up  the  stem  as  well 
as  with  conduction  by  the  sieve  vessels.  If  a  small  portion 
of  the  bark  is  removed,  the  incision  extending  only  to  the 
wood,  as  in  the  making  of  inscriptions  on  trees,  the  wound 
is  healed,  unless  too  large,  by  the  growth  of  tissue  from  all 
sides  until  it  is  closed  over.  In  this  new  tissue  a  cork 
cambium  is  developed,  and  presently  there  may  be  no 
surface  indication  of  the  wound.  But  if  the  wound 
has  gone  deeper  and  entered  the  wood,  the  record  of 
it  may  always  be  found  m  the  wood  by  removing  the 


56 


A  TEXT-BOOK  OF  BOTANY 


bark.     In  this  way  old  inscriptions  have  often  been  un- 
covered. 

The   well-known   operation   of  grafting  depends  upon 
the  ability  of  plants  to  heal  wounds.     The    plant   upon 

which    the   operation   is 
performed  is  called    the 
4  t     stock,  and  the  twig  graft- 

M  I     ed  into  it  the  scion.     An 

%  m       ordinary  method,   called 

•  i        cleft-grafting,  is  to  cut  off 

E  M  the  stem  or  a  branch  of 
the  stock,  split  the  stump, 
insert  into  the  cleft  the 
wedge-shaped  end  of  the 
scion,  and  seal  up  the 
wound  with  wax  or  clay. 
The  cambiums  of  the 
stock  and  the  scion  must 
be  put  into  contact  at 
some  point;  and  hence  it 
is  usual  to  insert  a  scion 
in  each  side  of  the  cleft, 
since  the  cambium  of  the 
stock  is  comparatively 
near  the  surface  (Fig.  55).  The  cambium  of  stock  and 
scion  unite,  the  wound  heals,  and  the  scion  becomes  as 
closely  related  to  the  activities  of  the  stock  plant  as  are 
the  ordinary  branches.  The  scions  are  usually  cut  in  the 
fall,  after  the  leaves  have  fallen,  are  kept  through  the  winter 
in  moist  soil  or  sand,  and  the  grafting  is  done  in  the  spring. 
A  number  of  important  things  are  secured  by  grafting,  but 
chief  among  them  is  the  perpetuation  of  useful  varieties 
with  certainty  and  at  a  great  saving  of  time. 

(2)   Monocotyledons. — In  this  great  group  of  plants  tne 
vascular  bundles  of  the  stem  are  not  arranged  so  as  to  form 


A  B 

FIG.  55. — Cleft-grafting  showing  scions  in 
place  (A)  and  the  wound  sealed  with 
clay  or  wax  (B). 


STEMS 


57 


Fio.  56. — A  corn-stalk,  show- 
ing in  cross  -  section  and 
longitudinal  section  the 
scattered  vascular  bundles. 


a  hollow  cylinder,  but  are  more  or  less  irregularly  scattered, 
as  may  be  seen  in  a  cross-section  of  a  corn-stalk  (Fig.  56). 
As  a  consequence,  there  is  no  en- 
closing of  a  definite  pith,  nor  is 
there  any  distinctly  bounded  cor- 
tex. In  the  bundles  there  is  no 
cambium,  and  therefore  new  wood 
and  bast  cannot  be  added  to  the 
old,  so  that  in  the  trees  there  is  no 
annual  increase  in  diameter;  and 
this  means  that  there  is  no  branch- 
ing and  no  increased  foliage  from 
year  to  year.  A  palm  well  illus- 
trates this  habit,  with  its  columnar, 
unbranching  trunk,  and  its  crown 
of  leaves,  which  continue  about  the  same  in  number  each 
year. 

25.  Ascent  of  sap. — The  water  entering  the  plant  by  the 
roots  and  .moving  upward  through  the  stem  is  usually 
called  sap.  It  is  not  pure  water,  but  contains  certain  soil 
substances  dissolved  in  it.  In  low  plants,  as  most  annuals, 
the  ascent  of  sap  requires  no  special  explanation;  but  in 
plants  such  as  trees,  in  which  the  crown  of  leaves  is  many 
feet  above  the  soil,  the  case  is  very  different.  Several 
explanations  of  the  ascent  of  sap  in  trees  have  been  sug- 
gested, and  all  have  been  disproved,  so  that  we  are  as  yet 
entirely  in  the  dark  as  to  the  method. 

That  the  path  of  ascent  is  through  the  vessels  of  the 
wood,  and  not  through  cortex  or  bast  or  pith,  may  be 
demonstrated  by  a  simple  experiment.  A  stem  of  corn 
or  sunflower  or  balsam  is  cut  off  and  placed  in  water  for 
an  hour.  Then  it  is  transferred  to  a  vessel  containing 
water  stained  with  cheap  red  ink  (a  solution  of  eosin), 
and  exposed  to  diffuse  light.  A  few  hours  later,  sections 
of  the  stem  will  show  the  wood  vessels  stained  red,  the 


58  A  TEXT-BOOK  OF  BOTANY 

ascending  water  having  stained  its  path.  Of  course  the 
stain  may  spread  somewhat  into  adjacent  cells. 

In  most  trees,  as  the  mass  of  wood  increases  in  diameter, 
the  ascending  sap  abandons  the  inner  (older)  wood  and 
moves  only  through  the  newer  wood.  This  results  in  a 
different  appearance  of  the  two  regions,  the  old  centra! 
wood,  abandoned  by  the  sap,  becoming  darker  and  often 
characteristically  colored  (heart  wood);  and  the  younger 
outer  wood,  used  by  the  sap,  being  lighter  colored  (sap 
wood).  Trees  vary  greatly  in  the  relative  thickness  of  the 
sap  wood;  for  example,  in  the  beech  it  is  a  thick  zone,  while 
in  the  oak  it  is  a  narrow  one.  In  successful  girdling  this 
must  be  taken  into  account,  since  an  incision  which  would 
cut  off  the  water  supply  of  an  oak  sufficiently  to  kill  it 
would  not  kill  a  beech. 

The  rate  of  movement  of  the  ascending  sap  of  course 
varies  with  different  plants  and  different  conditions.  In 
the  pumpkin-vine,  in  which  the  movement  is  very  rapid, 
it  has  been  found  to  reach  about  twenty  feet  an  hour.  It 
is  estimated  that  in  ordinary  broad-leaved  trees  the  rate  is 
probably  three  to  six  feet  an  hour. 

If  certain  stems  are  cut  off  near  the  ground,  it  is  ob- 
served that  after  a  short  time  the  sap  begins  to  ooze  out — 
a  phenomenon  that  is  often  called  bleeding.  In  some 
woody  plants,  as  grape-vines  and  birches,  the  sap  flows 
out  with  considerable  force,  indicating  some  pressure  be- 
low, which  is  called  root-pressure.  While  root-pressure  may 
force  the  sap  into  the  stem,  it  is  entirely  inadequate  to 
force  it  to  the  top  of  a  tree. 

The  so-called  maple  sap  obtained  from  the  sugar- 
maple  is  an  interesting  illustration  of  the  use  of  sap  that 
accumulates  in  a  woody  stem  in  the  spring.  At  that  time 
the  water  has  no  opportunity  to  escape  through  leaf  trans- 
piration; so  the  wood  becomes  gorged  with  sap,  which  can 
be  drawn  off  by  boring  into  the  wood  and  inserting  spiles. 


STEMS 


59 


The  characteristic  sugar  has  been  obtained  by  the  sap  from 
food  stored  in  the  stem,  notably  in  the  older  wood. 

26.  Growth  in  length. — Growth  in  length  begins  at  the 
tip  of  the  stem  by  the  formation  of  new  cells,  which  are 
organized  into  alternating  nodes  and 

internodes.  When  these  regions  are 
first  formed  the  internodes  are  very 
short,  and  their  subsequent  elonga- 
tion, separating  the  nodes,  is  the  chief 
cause  of  the  lengthening  of  the  stem. 
Internodes  are  able  to  elongate  for 
only  a  certain  time,  so  that  the  elon- 
gating portion  of  a  stem  does  not  often 
extend  more  than  ten  to  twenty  inches 
below  the  tip.  Seedlings  such  as  those 
of  the  bean  should  be  cultivated,  and 
the  region  of  growth,  the  region  of 
greatest  growth,  and  the  rate  of  growth 
determined.  The  same  method  may 
be  used  as  was  used  with  the  leaf 
(§  16),  in  this  case  each  internode 
being  marked  with  equally  spaced  lines 
in  India  ink.  Measuring  these  spaces 
at  intervals  of  one  or  two  days  will 
determine  the  facts  referred  to  above 
(Fig.  57). 

27.  Special  forms  of  stems. — Usu- 
ally branches  resemble  the  stem  from 
which  they  arise,  but  occasionally  they 

differ  in  a  striking  way.  That  these  different  structures  are 
really  branches  is  usually  evident  to  external  observation 
from  the  fact  that  they  stand  in  the  position  of  branches, 
that  is,  in  the  axils  of  leaves  (§  22).  The  three  following 
forms  illustrate  axillary  structures  that  do  not  resemble 
ordinary  branches. 


FIG.  57. — Scarlet  runner 
bean  marked  with  a 
scale  of  five  millimeter 
intervals  and  photo- 
graphed after  forty- 
eight  hours ;  the  lines 
closest  together  show 
the  original  spacing. 


60  A  TEXT-BOOK  OP  BOTANY 

/ 

(1)  Cladophylls. — If  the  greenhouse  smilax,  often  called 
wedding  smilax,  be  examined,  the  apparent  leaves  will  be 
discovered  to  be  branches  modified  so  as  to  assume  the 
form  and  work  of  leaves,  each  one  of  these  leaf-like  branches 
standing  in  the  axil  of  a  minute  scale-like  leaf  (Fig.  58,  A). 
Such  branches  are  called  cladophylls,  which  means  "  leaf-like 


B 


FIG.  58. — Cladophylls:  A,  wedding  smilax  (the  apparent  leaves  are  the  modified 
branches,  and  the  real  leaves  are  the  minute  scales  that  subtend  them);  B, 
Phyllocladus. 

branches."  In  the  Australian  region  a  group  of  evergreens 
is  characterized  by  bearing  cladophylls;  and  the  young 
plantlet  shows  the  gradual  change  of  true  green  leaves 
into  little  scales,  and  of  branches  into  cladophylls  (Fig. 
58,  B).  In  the  common  garden  asparagus  the  apparent 
slender,  needle-like  leaves  are  all  cladophylls  doing  leaf 
work. 

(2)  Tendrils. — It  was  shown  (§  20)  that  leaves  or  parts 
of  leaves  may  develop  as  tendrils,  and  this  is  true  also  of 


STEMS  61 

branches,  as  observed  in  the  passion-flower,  whose  long 
and  very  sensitive  tendrils  appear  in  the  axils  of  the  leaves 
(Fig.  59).  Whether  tendrils  replace  leaves  or  branches 


FIG.  59. — Plants  of  passion-flower  showing  axillary  tendrils. 

makes  no  difference  as  to  their  structure  and  activity,  but 
it  is  of  interest  to  note  that  different  organs  may  thus  be 
replaced  by  the  same  organ. 


62 


A  TEXT-BOOK  OF  BOTANY 


(3)  Thorns. — Branches,  as  well  as  leaves  (§  20),  may 
develop  as  thorns;  an  excellent  illustration  of  a  branching 
thorn  being  seen  in  the  honey  locust  (Fig.  60,  A),  and  of  a 
simple  thorn  in  hawthorn  (Fig.  60,  B).  In  dry  regions, 


' 


A  V.      B 

FIG.  60. — Thorns:     A,  honey  locust;  B,  hawthorn. 

such  as  may  be  found  along  the  Mexican  border,  thorns  and 
spiny  branches  are  very  common;  and  since  in  some  cases 
these  spiny  branches  develop  into  ordinary  branches  when 
the  plant  has  a  sufficient  supply  of  water,  it  is  thought  that 
such  thorns  and  spines  are  results  of  unfavorable  conditions 
for  growth.  The  same  statement  applies,  of  course,  to  those 
cases  in  which  thorns  have  replaced  leaves. 

The  most  common  modifications  of  the  stem  are  those 
which  arise  when  it  is  an  underground  structure.  Although 
it  is  natural  to  think  of  all  underground  structures  as  roots, 
this  is  far  from  being  true.  Since  the  stem  is  primarily  a 


STEMS  63 

leaf-bearing  structure,  it  continues  to  bear  leaves  when 
under  ground;  but  often  these  leaves  are  much  modified, 
either  reduced  in  size  so  as  to  be  mere  rudiments,  or  used 
for  some  other  purpose.  The  fact  that  a  subterranean 
structure  bears  leaves  of  some  kind  indicates  that  it  is  a 
stem  and  not  a  root.  Since  both  the  stem  and  its  leaves 
must  be  considered  in  connection  with  the  underground 
habit,  the  shoot  (§21)  will  be  considered  rather  than  the 
stem  alone.  In  general  the  subterranean  shoot  is  con- 
spicuously a  region  of  food  storage.  The  three  following 
types  are  the  most  common. 

(4)  Rhizomes. — This  is  probably  the  most  common 
form  of  subterranean  stem.  It  is  usually  horizontal,  more 
or  less  elongated,  and  much 
thickened  for  food  storage,  and 
is  often  called  the  rootstock 
(Fig.  61).  It  advances  through 
the  soil  year  after  year,  often 
branching,  sending  out  roots  be- 
neath and  leaf-bearing  branches 
into  the  air.  As  it  continues  to 
grow  at  the  apex,  it  gradually 
dies  behind, 
thus  isolating 
branches  in 
the  case  of 
branching  rhi- 
zomes. It  is 
a  very  efficient 

method  for  the  ^I0<  61- — Rootstock  °f  a  fern  (common  brake), 

bearing  young  leaves. 

spreading      of 

plants  and  is  extensively  used  by  grasses  in  covering  areas 
and  forming  turf.  The  persistent  continuance  of  some 
weeds,  especially  certain  grasses  and  sedges  that  infest 
lawns  and  meadows,  is  due  to  this  habit  (Fig.  62).  It  is 


\ 


A  TEXT-BOOK  OF  BOTANY 


impossible  to  remove  from  the  soil  all  of  the  indefinitely 
branching  rhizomes,  and  any  nodes  that  remain  are  able 
to  send  up  fresh  crops  of  aerial  branches.  In  many  cases 


FIG.  62.  —  Rootstock  of  a  Juncus,  showing  how  it  advances  beneath  the  ground 
and  sends  up  a  succession  of  branches;  the  breaking  up  of  such  a  rootstock  only 
results  in  separate  individuals. 

only  a  single  aerial  branch  is  sent  up  each  year,  as  in  wild 
ginger,  Solomon's  seal   (Fig.  63),  iris,  bloodroot,  etc.;   in 

others,  leaves 
and  flowers 
may  be  sent  up 
separately  by 
the  rhizome. 
In  the  com- 
mon ferns,  it 

FIG.  63.—  Rootstock  of  Solomon's  seal,  showing  terminal  Will  be  noted, 
bud,  the  base  of  this  year's  aerial  branch,  and  scars  of 


the  branches  of  three  preceding  years.  —  After  GRAY. 


^Jjg     QQ  _  called 

fronds  are  sim- 

ply large  leaves  developed  directly  by  the  rhizome.     Per- 
haps even  more  familiar  is  the  extensive  rhizome  system 


STEMS  65 

of  the  water-lilies,  from  which  arise  the  leaves  with  large 
floating  blades  (pads).  Therefore,  a  rhizome  does  not  nec- 
essarily bear  only  scale  leaves,  but  may  develop  also  leaves 
that  become  aerial;  and  in  that  case  they  are  usually 
large.  It  is  evident  that  in  plants  possessing  rhizomes 
the  subterranean  stems  are  perennial,  while  the  aerial  parts 
may  be  annual. 

(5)  Tubers. — In  some  plants  the  ends  of  underground 
stems  become  very  much  enlarged  for  food  storage.  These 
enlargements  are  called  tubers,  the  best-known  illustration 
being  the  common  potato  (Fig.  64).  That  it  is  a  stem 
structure  is  evident  from  the  fact  that  it  bears  very  much 


Flo.  64. — Potato  tuber    showing  eyes  (scale  leaves  and  axillary  buds). 

reduced  leaves,  in  the  axils  of  which  are  buds,  the  so-called 
"eyes."  Abnormally  developed  potatoes  often  show  the 
shoot  character  of  the  tuber  very  plainly,  and  in  the  case 
of  potatoes  sprouting  it  is  evident  that  the  eyes  have  de- 
veloped into  branches.  In  planting  potatoes,  advantage  is 
taken  of  the  fact  that  any  node  placed  in  proper  conditions 
may  strike  root  and  put  out  a  branch.  Since  the  eyes  are 
branch  buds  standing  at  nodes,  and  any  piece  of  the 
potato  containing  a  bud  is  able  to  produce  a  new  plant,  it  is 
customary  to  cut  the  potato  into  pieces,  being  careful  that 
each  piece  contains  one  or  more  eyes.  Heaping  up  the 
soil  (hilling  up)  about  the  base  of  the  potato  plant  induces 
the  formation  of  more  of  the  subterranean,  tuber-bearing 


66 


A  TEXTrBOOK  OF  BOTANY 


branches.  In  the  tuber  called  Jerusalem  artichoke,  which  is 
developed  by  the  subterranean  stems  of  a  kind  of  sunflower, 
the  nodes  of  the  stem  and  the  buds  of  branches  are  more 
conspicuous  than  in  the  potato.  Fleshy  roots,  such  as  those 
of  the  sweet  potato,  should  not  be  confused  with  tubers. 

(6)  Bulbs. — In  some  plants  the  main  stem  is  very  short 
and  is  covered  by  numerous  thickened,  overlapping  leaves 
or  leaf  bases  (usually  called  scales),  the  whole  structure 

being  a  bulb.  Bulbs 
such  as  those  of  the 
lily,  hyacinth,  tulip,  and 
onion  are  very  familiar. 
In  this  case  the  food 
storage  is  chiefly  in  the 
scales.  Scaly  bulbs  are 
those  in  which  the  scales 
overlap,  but  are  not 
broad  enough  to  enwrap 
those  within,  as  the  lily 
bulb  (Fig.  65);  coated 
bulbs  are  those  in  which 
the  broad  scales  com- 
pletely enwrap  those 
within,  as  the  bulbs 
of  onions  and  tulips. 

Small  bulbs,  called  bulblets,  are  borne  by  some  plants  on 
parts  above  ground;  as,  for  example,  the  bulblets  that  ap- 
pear in  the  axils  of  the  leaves  of  the  tiger-lily  and  those  that 
replace  flower-buds  in  the  common  onion.  These  bulblets, 
when  planted,  have  the  power  of  producing  new  plants,  as 
do  the  subterranean  bulbs. 

The  above  subterranean  shoots,  with  their  storage  of 
reserve  food,  enable  plants  to  put  out  their  aerial  parts  with 
remarkable  promptness  and  develop  them  with  great 
rapidity.  As  an  illustration  of  a  situation  in  which  this 


FIG.  65.— Scaly  bulb  of  white  lily:  A,  exte- 
rior view;  B,  longitudinal  section,  showing 
short  stem  and  overlapping  scales. — After 
BAILLON 


STEMS  67 

ability  is  of  great  advantage  to  plants,  the  vernal  habit  may 
be  mentioned.  It  is  a  matter  of  common  observation  that 
the  rich  display  of  spring  flowers  occurs  in  forests  and 
wooded  glens  before  the  trees  come  into  full  foliage.  The 
working  season  of  these  spring  plants  is  between  the  begin- 
ning of  the  growing  season  and  the  full  forest  foliage,  and 
the  subterranean  shoots  enable  them  to  send  up  branches  or 
leaves  with  great  rapidity.  After  the  forest  leaves  are  fully 
•developed,  the  available  light  for  work  beneath  the  forest 
crown  diminishes,  the  spring  flowers  disappear,  and  the  short 
period  of  activity  does  not  return  until  the  next  season. 

It  has  been  observed  that  many  of  these  underground 
structures  gradually  become  more  and  more  deeply  buried, 
.and  it  appears  that  some  process  of  self-burial  is  going  on. 
For  example,  it  has  been  observed  that  if  the  tuberous 
underground  stem  of  Jack-in-the-pulpit,  often  called  In- 
dian turnip,  be  planted  in  a  flower-pot  near  the  surface  of 
the  soil,  it  will  be  found  six  inches  deeper  within  a  week. 
This  is  probably  an  illustration  of  exceedingly  rapid  burial, 
but  enough  has  been  observed  of  the  habits  of  such  plants 
to  indicate  that  such  gradual  self-burial  of  underground 
parts  is  very  common.  Experiments  have  indicated  that 
this  self-burial  is  not  continued  indefinitely,  but  that  for 
•each  kind  of  plant  there  is  a  normal  depth  reached  by  the 
underground  stems.  If  such  stems  are  planted  below 
their  normal  depth,  the  experiments  show  that  there  are 
various  methods  of  ascending  to  the  proper  depth. 

BUDS 

.28..  Mature  of  buds. — A  bud  is  an  undeveloped  shoot, 
whose  internodes  have  not  elongated,  so  that  the  leaves 
overlap,  forming  a  more  or  less  compact  structure  (Fig.  66). 
It  resembles  a  bulb  or  bulblet  in  general  structure,  except 
that  the  overlapping  leaves  are  not  thickened  as  food 
reservoirs.  The  outer  (older)  leaves  of  the  bud  protect  the 


68 


A  TEXT-BOOK  OF  BOTANY 


inner  (younger)  ones,  and  all  the  leaves  protect  the  delicate 
growing  apex  of  the  stem  or  the  branch.  There  are  what 
are  called  leaf-buds  and  flower-buds,  but  only  the  former 
will  be  considered  here. 

29.  Position  of  buds. — In  shrubs  and  trees  the  growth 
of  stem  and  branches  is  not  continuous,  but  is  interrupted 
during  the  winter.  Preparatory  to  this 
interruption  a  bud  is  formed  at  the  end  of 
each  growing  axis,  and  is  called  the  termi- 
nal bud  (Fig.  66).  When  it  opens  the  fol- 
lowing season  it  continues  the  growth  of 
the  stem  or  branch.  Buds  are  formed  also 
in  the  axils  of  leaves,  usually  one  bud  in 
an  axil,  and  hence  they  are  called  axil- 
lary buds  (Fig.  66).  When  they  develop 
they  form  new  branches.  When  the  ter- 
minal buds  are  stronger  than  the  axillary 
buds,  the  main  stem  or  branches  continue 
to  elongate  year  after  year;  but  if  the 
axillary  buds  are  stronger,  the  growth  of 
the  new  branches  may  replace  that  of  the 
stem  from  which  they  arise.  For  exam- 
ple, in  the  common  lilac  the  two  buds  in 
the  axils  of  the  uppermost  opposite  leaves 
develop  branches,  the  terminal  bud  be- 
tween them  not  continuing  the  growth 
of  the  axis,  and  often  not  even  being 
formed.  Hence  the  lilac  bush  is  charac- 
terized by  its  forked  branching,  each  axis  appearing  to  end 
in  a  pair  of  branches.  Axillary  buds  do  not  all  develop  into 
branches  by  any  means,  but  any  of  them  may  do  so  under 
certain  conditions.  If  the  terminal  bud  is  injured  or  is  fee- 
ble, the  axillary  bud  or  buds  nearest  to  it  will  be  more 
likely  to  develop  branches;  and  if  the  upper  axillary  buds 
are  injured,  the  next  lower  ones  will  develop,  and  so  on 


FIG.  66.— Scaly  buds 
of  hickory;  termi- 
nal one  strongest; 
lateral  ones  axil- 
lary as  shown  by 
the  leaf  scars. — 
After  GRAY, 


STEMS  69 

down  the  axis.  Axillary  buds  may  exist  for  several  years 
without  any  opportunity  to  develop,  and  they  may  even  be 
overlaid  by  the  growth  of  the  stem  on  which  they  stand. 

30.  Scaly  buds. — The  most  conspicuous  buds  are  the 
so-called  scaly  buds,  in  which  the  outermost  leaves  develop 
as  dry  and  often  hard  scales,  entirely  unlike  the  true  leaves 
(Fig.  66).     These  overlapping  scales  protect  the  delicate 
leaves  within  and  the  growing  apex  of  the  stem  from  sudden 
changes  of  temperature  and  from  moisture,  and  are  often 
made  still  more  effective  against  moisture  by  becoming 
covered  with  a  sort  of  varnish  or  balsam,  as  in  the  horse- 
chestnut  and  balsam-poplar.     The  inside  of  the  scales  or 
the  young  leaves  within  are  often  covered  with  wool,  as  a 
further  protection  against  sudden  changes  of  temperature. 
It  is  evident  that  scaly  buds  are  especially  adapted  to 
protect   delicate   structures  during  the   winter  and  early 
spring,  and  hence  are  characteristic  of  the  shrubs  and  trees 
of  temperate  regions. 

In  the  spring,  such  buds  first  swell  and  then  open,  the 
young  branch  emerging  by  the  lengthening  of  its  inter- 
nodes,  and  gradually  spreading  its  leaves.  During  the 
opening  the  scales  usually  drop  off,  leaving  more  or  less 
complete  rings  of  scars  about  the  stem,  thus  permanently 
marking  the  position  of  the  bud.  If  a  branch  continues 
to  elongate  for  a  number  of  years,  its  age  and  the  amount 
of  growth  each  year  can  be  determined  by  the  successive 
sets  of  bud  scars. 

31.  Naked  buds. — Buds  in  which  no  protective  scales  are 
developed,  or  any  other  special  coverings,  are  called  naked 
buds,  and  are  characteristic   of  tropical   plants,   although 
not  entirely  lacking  in  plants  of  the  temperate  regions. 

32.  Accessory  buds. — In  some  plants  more  than  one 
bud  may  appear  in  the  axil  of  a  leaf,  as  in  the  maples,  in 
which  three  buds  occur  side  by  side  (Fig.  67).     As  these 
buds  are  most  conspicuous  in  the  early  spring,  the  position 


70 


A  TEXT-BOOK  OF  BOTANY 


of  the  leaf  is  indicated  by  the  leaf  scar,  immediately  above 
which  the  three  buds  appear.  In  the  common  bush  honey- 
suckle, three  to  six  buds  appear  in  each  axil. 
In  all  such  cases  the  extra  buds  are  called 
accessory  buds. 

33.  Adventitious  buds. — Since  the  tips  of 
stems  or  branches  and  the  axils  of  leaves  are 
the  usual  places  for  buds,  those  which  occur 
in  other  positions  are  called  adventitious  buds. 
Such  buds  appear  on  stems  (on  the  inter- 
nodes),  roots,  and  even  leaves,  and  very 
commonly  they  arise  as  a  result  of  injury. 
On  the  trunks  of  trees,  even  at  the  base, 
wounds  often  result  in  the  formation  of  buds 
and  the  development  of  vigorous  young 
branches,  usually  called  suckers  or  water 
sprouts.  Often  from  a  stump  young  shoots 
arise,  and  the  process  of  pollarding  consists 
in  cutting  off  the  crowns  of  trees  that  new 
branches  may  be  developed  in  connection 
with  the  wound.  In  the  willows,  for  example, 
the  production  of  such  shoots  is  so  prompt 


FIG.  67.— Branch 
of  maple,  show- 
ing terminal, 

lateral,  and  ac-    and  they   are  so  vigorous  and  pliable  that 
twigs  for  basket-work  are  obtained  from  them 


cessory  buds. — 
After  GRAY. 

in  this  way.  In  propagating  plants  by  root- 
cuttings,  as  can  be  done  with  blackberries  and  raspberries, 
advantage  is  taken  of  the  fact  that  some  roots  can  produce 
buds.  In  propagating  by  stem-cuttings  it  is  the  axillary 
buds  that  develop  the  new  shoots;  but  in  root-cuttings  the 
new  shoots  arise  from  adventitious  buds.  That  leaves  also 
may  produce  adventitious  buds  is  shown  in  connection  with 
the  practise  of  propagating  begonias  by  leaf-cuttings. 

It  is  evident,  therefore,  that  while  plants  ordinarily 
produce  terminal  and  axillary  buds,  under  certain  con- 
ditions buds  may  be  developed  and  shoots  arise  at  any  place. 


CHAPTER  IV 

ROOTS 

34.  General  character. — In  general,  roots  are  organized 
to  work  in  the  soil,  but  this  is  not  true  of  all  of  them.  The 
soil  roots,  however,  will  be  considered  first,  as  being  the 
most  common  and  as  exhibiting  most  clearly  the  structure 


FIG.  68. — Roots:  .A , dandelion  with  tap-root;  B.  grass  with  cluster  of  fibrous  roots. 

6  71 


A   TEXT-BOOK  OF  BOTANY 


and  work  of  roots.  One  of  the  most  obvious  contrasts 
with  the  stem  in  external  appearance  is  that  roots  bear  no 
leaves  or  scales,  and  are  not  made  up  of  nodes  and  inter- 
nodes. 

The  root  that  comes  from  the  seed,  including  all  of  its 
subsequent  branches,  is  the  primary  root.  In  some  cases 
the  primary  root  develops  a  single  prominent  vertically 
descending  axis,  called  the  tap-root,  which  gives  off  small 
branches,  as  in  the  dandelion  (Fig.  68,  A);  in  other  cases 
the  primary  root  breaks  up  at  once  into  a  cluster  of  branches, 
as  in  many  grasses  (Fig.  68,  B).  In  many  cases  the  tap- 
root becomes  conspicuously  thickened  for  food  storage,  as 

illustrated  by  such  common 
vegetables  as  radish  (Fig.  69, 
A),  turnip,  and  parsnip.  In 
some  cases  where  there  is  no 


FIG. 


).— Fleshy  roots:  A,  radish  with  fleshy  tap-root;  B,  dahlia  with  cluster  of 
fleshy  roots 


tap-root,  the  branches  become  thickened,  forming  such 
clusters  of  thickened  roots  as  those  of  the  dahlia  (Fig.  69, 
B}  and  of  the  sweet  potato.  Roots  that  arise  from  the 
stem  or  the  leaves  are  secondary  roots.  For  example,  a 
subterranean  stem  or  a  creeping  stem  strikes  root  from  the 


ROOTS 


73 


nodes,  and  such  secondary  roots  may  be  the  only  roots  of 
many  plants  (Fig.  46).  In  propagating  plants  by  layering 
(§  23)  or  by  cuttings,  the  roots  are  necessarily  all  secondary 
roots.  Even  erect  stems 
sometimes  send  down 
secondary  roots  into  the 
soil  from  the  lower  joints 
(Fig.  77),  as  is  very  com- 
mon in  corn. 

35.  Root-cap.  —  The 
growing  tip  of  each  root 
and  rootlet  is  protected 
by  a  cap  of  cells  called 
the  root-cap  (Fig.  70). 
This  root-cap  consists  of 
several  layers  of  cells, 
the  outer  ones  gradually 
dying  or  being  worn  away 
as  the  tip  of  the  root 
pushes  through  the  soil, 
and  being  replaced  by 
new  layers  which  are 
continually  forming  be- 
neath. In  some  plants 
the  root-cap  is  very 
easily  seen  as  a  conical 
thickening  at  the  tip  of 
the  root;  in  others  it 
can 

only  by  examining  un- 
der the  microscope  lon- 
gitudinal sections  through  the  root-tip.  The  presence  of 
such  a  protective  cap  in  the  root  is  in  strong  contrast  with 
the  stem,  whose  growing  tips  are  protected  by  overlapping 
leaves. 


i  j  i      FIG.  70. — Longitudinal    section    through  root- 

be     demonstrated       tip  of  8piderwortt  showing  central  vascular 

axis    (pi),    cortex    (p),    epidermis    (e),   and 
root-cap  (c). 


74 


A  TEXT-BOOK  OF  BOTANY 


36.  Root-hairs. — A  short  distance  behind  the  root-cap 
the  surface  of  the  root  becomes  covered  by  a  more  or  less 
dense  growth  of  hairs,  known  as  root-hairs  (Fig.  71).  These 

hairs  are  outgrowths,  some- 
times very  long  ones,  from  the 
superficial  cells,  a  single  cell 
producing  a  single  root-hair. 
In  fact  the  root-hair  is  only  an 
extended  part  of  the  superfi- 
cial cell.  The  root  absorbs 
water  and  materials  dissolved 
in  it  from  the  soil,  and  the 
root-hairs  enormously  increase 
the  absorbing  surface.  Gen- 
erally root-hairs  do  not  last 
very  long;  but  new  hairs  are 
being  put  out  by  the  elonga- 
ting root  as  the  old  ones  behind 

root-hairs  and  their  position  in  ref-      <}ie>  so   that  there    is    always  a 
erence  to  the  growing  tip:  A,  grown 
in  soil  (higher  up  the  hairs  become 
much  more  abundant  and  longer); 
B,  grown  in  moist  air. 


FIG.  71. — Root-tips  of  corn,  showing 


zone  of  active  root-hairs  near 
the  tip,  but  none  on  the  older 
parts  of  the  root. 
37.  Internal  structure. — A  cross-section  of  a  young  root 
shows  two  prominent  regions  (Fig.  73).  In  the  center  is  a 
solid"  vascular  cylinder,  often  called  the  central  axis.  It 
will  be  remembered  that  in  the  stems  of  Dicotyledons  and 
Gymnosperms  (§  24)  the  vascular  cylinder  is  hollow,  en- 
closing pith.  Investing  the  solid  vascular  cylinder  of  the 
root  is  the  cortex,  which  often  can  be  stripped  from  the 
central  axis  like  a  spongy  bark.  If  the  section  has  passed 
through  the  zone  of  root-hairs,  they  can  be  seen  coming 
from  the  superficial  cells.  A  longitudinal  section  of  a  root- 
tip,  in  which  these  regions  are  very  young,  is  shown  in 
Fig.  70. 

The  wood  (xylem)  and  the  bast  (phloem)  of  the  vascular 


ROOTS 


75 


cylinder  do  not  hold  the  same  relation  to  each  other  as  in 
the  stem  (§  24).  The  vascular  cylinder,  instead  of  being 
made  up  of  vascular  bundles 
with  wood  toward  the  center 
and  bast  toward  the  outside, 
as  in  stems,  is  made  up  of 
wood  and  bast  strands  alter- 
nating with  each  other  around 
the  center  (Fig.  72).  The 
wood  strands  radiate  from 
the  center  like  the  spokes  of 
a  wheel,  and  the  bast  strands 
are  between  these  spokes  near 
their  outer  ends.  This  ar- 
rangement of  wood  and  bast 
is  peculiar  to  roots. 

When  roots  increase  in  diameter,  a  cambium  soon  begins 
to  form  new  wood  and  bast,  as  in  the  stems  that  increase 


FIG.  72. — Diagrammatic  cross-section  of 
a  young  root,  showing  the  innermost 
layer  of  the  cortex  (c)  and  the  vascu- 
lar cylinder  (t>)  containing  alternating 
regions  of  xylem  (z~)  and  phloem  (p). 


B  A 

FIG.  73. — Diagram  showing  the  method  of  thickening  the  vascular  cylinder  of  a  root : 
A  represents  the  cross-section  of  a  young  root  in  which  four  phloem  strands  (p) 
alternate  with  four  xylem  strands  (x),  the  whole  bundle  region  being  enveloped 
by  the  thick  cortex  ;  B  represents  an  older  root  in  which  there  is  a  continuous  zone 
of  cambium  (c),  which  is  forming  on  the  outside  new  phloem  (np)  in  contact 
with  the  old  Op),  and  on  the  inside  new  xylem  (nz)  alternating  with  the  old  (x)» 


76 


A  TEXT-BOOK  OF  BOTANY 


in  diameter  (§  24).  The  new  wood,  however,  is  not  formed 
in  connection  with  the  old  wood,  but  just  within  the  bast, 
that  is,  farther  in  between  the  " spokes"  of  old  wood, 
resulting  in  bundles  like  those  of  the  stem  (Fig.  73).  In 
this  way  a  thickening  vascular  cylinder  is  formed,  like  that 
of  stems  that  increase  in  diameter;  and  presently  the  cross- 
section  of  the  root  resembles  that  of  the  stem.  It  is  evident 
(Fig.  73)  that  the  principal  pith  rays  separating  the  vas- 
cular bundles  of  such  a  root  extend  inward  to  the  original 
radiating  strands  of  wood  that  alternate 
with  the  original  strands  of  bast.  The  vas- 
cular bundles  of  the  root  connect  with  those 
of  the  stem,  and  these  in  turn  with  those  of 
the  leaves,  so  that  throughout  the  whole 
plant  there  is  a  continuous  vascular  system. 
The  origin  of  the  branches  of  roots  is  very 
different  from  that  of  stems.  In  a  stem 
the  branch  begins  at  the  outer  part  of  the 
cortex,  but  in  the  root  it  begins  at  the  sur- 
face of  the  vascular  cylinder  and  breaks 
through  the  cortex  (Fig.  74).  If  the  cor- 
tex of  a  root  be  stripped  off,  the  branches 
will  be  found  attached  to  the  central  axis, 
and  the  perforations  made  by  the  branches 
through  the  cortex  can  be  seen. 

38.  Growth  in  length. — The  elongating 
region  of  the  root  is  much  more  restricted 
than  that  of  the  stem.  It  was  stated  (§  26) 
that  the  elongating  region  of  a  stem  may 
extend  ten  to  twenty  inches  from  the  tip,  or  even  more; 
but  the  elongating  region  of  a  root  is  hardly  ever  more  than 
two-fifths  of  an  inch,  and  often  not  more  than  half  of  that. 
The  region  of  elongation  and  of  greatest  elongation  should 
be  determined  by  using  such  seedlings  as  those  of  peas, 
beans,  and  corn.  When  the  young  roots  have  become  a 


FIG.  74.— Longitu- 
dinal section  of 
root  of  arrow- 
leaf,  showing  the 
branches  start- 
ing from  the 
central  axis  and 
penetrating  the 
cortex. 


ROOTS 


77 


FIG.  75. — Roots  of  scarlet  -  runner  bean 
marked  with  lines  one  millimeter  apart 
and  photographed  after  forty -eight 
hours. 


half  to  one  inch  long,  mark  as  delicately  as  possible  in  India 
ink  with  a  soft  camePs-hair  brush  a  series  of  equally  spaced 
lines,  beginning  at  the  tip.     Observations  at  the  end  of 
twenty-four  to  forty-eight 
hours    will    discover    the 
region  of  elongation  and 
of      greatest      elongation 
(Fig.  75). 

39.  The  soil.— Before 
absorption  by  roots  is  con- 
sidered, it  is  necessary  to 
know  something  of  the 
structure  of  soil.  Soil  is 
finely  divided  rock  ma- 
terial, which  may  be 
mixed  with  a  greater  or 
less  amount  of  material 

(called  organic  material)  derived  from  the  broken-down 
bodies  or  waste  products  of  plants  and  animals.  However 
fine  the  particles  of  soil  may  be,  they  never  fit  together  in 
close  contact,  so  that  there  are  open  spaces  everywhere 
among  them.  Immediately  after  a  soaking  rain  these 
spaces  are  full  of  water,  but  if  the  soil  is  one  that  drains 
easily,  the  water  gradually  disappears  from  the  spaces,  and 
the  larger  ones  are  occupied  by  air.  In  addition  to  this 
occasional  water,  each  particle  of  soil  is  invested  by  a  thin 
film  of  water,  which  adheres  to  it  closely,  and  which  never 
entirely  disappears  even  in  the  driest  soil.  The  soil  water 
is  never  absolutely  pure,  but  contains  dissolved  in  it  cer- 
tain materials  obtained  from  the  soil. 

As  types  of  soil,  sand,  clay,  and  humus  may  be  con- 
sidered. Humus  is  a  soil  in  which  there  is  intermixed  a 
large  amount  of  decayed  plant  material;  and  it  is  frequently 
called  vegetable  mold,  or  leaf  mold,  the  best  illustration 
being  the  upper  soil  of  forests.  Aside  from  certain  materials 


78  A  TEXT-BOOK  OF  BOTANY 

that  the  different  soils  may  supply  to  the  plant,  they  are 
especially  characterized  by  their  relation  to  water.  The 
power  of  a  soil  to  receive  and  to  retain  water  is  a  very 
important  consideration  in  connection  with  plants.  For 
example,  it  is  evident  that  the  receptive  power  of  sand  is 
high,  and  its  retentive  power  is  low;  while  in  the  case  of 
clay  the  reverse  is  true.  One  of  the  great  advantages  of 
humus  is  that  its  receptive  and  retentive  powers  are  better 
balanced  than  in  sand  and  clay.  It  is  easy  to  devise  a 
series  of  experiments  that  will  show  in  a  rough  way  the 
comparative  receptive  and  retentive  powers  of  these  three 
types  of  soil.  It  has  been  shown  also  that  for  any  given 
soil,  the  more  finely  the  particles  are  divided  the  better  it  is 
for  plants.  When  the  soil  is  turned  up  with  plow  or  spade, 
it  is  dried  by  the  air  and  pulverized  and  so  put  in  better 
condition  for  plants. 

It  is  evident  that  in  considering  the  relation  of  the  soil 
to  plants,  not  only  the  surface  soil  must  be  considered,  but 
also  the  soil  beneath  (subsoil).  For  example,  if  humus 
rests  on  sand,  the  water  will  drain  away  much  more  rapidly 
than  if  humus  rests  on  clay.  The  whole  subject  of  the  soil 
in  its  relation  to  plants  is  one  of  extreme  complexity  and  is 
as  yet  little  understood. 

40.  Absorption  of  water. — To  obtain  water  from  the 
soil,  the  root  not  only  often  branches  profusely,  but  also 
develops  the  root-hairs  described  above  (§  36).  Only  in 
the  younger  portions  of  the  root,  that  is,  in  the  general  re- 
gion of  the  root-hairs,  is  absorption  of  water  effected.  The 
root-hairs  push  out  among  the  soil  particles  and  come  into 
very  close  contact  with  them,  the  particles  sometimes  be- 
coming embedded  in  the  wall  of  the  hair  (Fig.  76).  In  this 
way  the  films  of  water  adhering  to  each  soil  particle  are 
closely  applied  to  the  hair,  and  water  passes  from  them 
through  the  wall  of  the  hair  into  its  cavity,  and  so  into  the 
plant.  The  process  by  which  the  water  passes  in  is  known 


ROOTS 


79 


as  osmosis.     As  water  is  absorbed  from  the  films  they 

become  thinner,  and  this  loss  is  supplied  from  neighboring 

films.     In  this  way  a  flow  from  regions  of  the  soil  deeper 

and  more  distant  than  those  to  which 

the  root  reaches  is  set  up  toward  the 

films  losing  water.     The  water  supply 

may  not  be  able  to  make  good  such 

loss  indefinitely;  and  if  so,  the  films 

gradually    become    thinner,    until    a 

point  is  reached  when  the  root-hair 

can  obtain  no  more  water,  the  film 

holding  tenaciously  to  its  particle  of 

soil.     After  the  roots  have  obtained 

all  the  water  they  can  from  the  soil, 

and  it   seems   perfectly  dry,   it   still 

contains  two  to  twelve  per  cent  of 

water  in  the  form  of  films. 

The  water  thus  obtained  by  the 
root-hairs  passes  inward  through 
the  cortex  and  enters  the  wood 
of  the  vascular  cylinder,  and 
then  is  free  to  ascend  to  the 
wood  of  the  stem,  and  so  to  the 
leaves. 

It  should  be  understood  that  the  water  does  not  carry 
into  the  plant  the  soil  substances  dissolved  in  it;  but  each 
dissolved  substance,  although  it  must  be  in  solution  in 
order  to  enter  the  plant,  is  turned  back  or  enters  upon  con- 
ditions that  belong  to  itself  alone.  Certain  dissolved 
substances  may  not  be  able  to  enter  at  all,  and  in  con- 
sequence of  this  the  root  has  been  said  to  possess  a  selective 
power;  while  other  substances  may  enter  with  greater  or  less 
rapidity  at  different  times,  or  may  even  be  turned  back  at 
certain  times.  All  this  diversity  of  behavior  is  dependent 
upon  definite  laws  of  physics. 


FIG.  76.  —  Root-hair  of  wheat, 
which  is  shown  to  be  an  out- 
growth from  an  epidermal 
cell,  in  close  contact  with  soil 
particles. 


80  A  TEXT-BOOK  OF  BOTANY 

41.  Special  forms  of  roots. — Roots  in  the  soil  serve  the 
double  purpose  of  anchoring  the  plant  and  absorbing  wa- 
ter, but  certain  roots  hold  other  relations  and  need  special 
mention. 

(1)  Prop  roots. — In  certain  plants  roots  are  sent  out 
from  the  stem  or  the  branches,  and  finally  reaching  the 
ground  establish  the  usual  soil  relations.     Since  these  roots 
resemble  braces  or  props,  the  name  prop  roots  has  been  ap- 

•  .plied  to  them  (Fig.  77).  A  very  common  illustration  is 
that  of  the  corn-stalk,  which  sends  out  such  roots  from  the 
lower  nodes  of  the  stem.  More  striking  illustrations,  how- 
ever, are  furnished  by  the  banyan  and  the  mangrove.  The 
banyan  sends  down  from  its  wide-spreading  branches  prop 
roots,  which  are  sometimes  very  numerous.  When  they 
enter  the  soil  they  often  grow  into  large  trunk-like  sup- 
ports, enabling  the  branches  to  extend  over  an  extraordi- 
nary area.  There  is  record  of  a  banyan  cultivated  in 
Ceylon  with  350  large  and  3,000  small  prop  roots,  and 
able  to  cover  a  village  of  one  hundred  huts.  The  man- 
grove is  found  along  tropical  and  subtropical  seacoasts, 
and  gradually  advances  into  the  shallow  water  by  drop- 
ping prop  roots  from  its  branches  and  entangling  the 
detritus  (Fig.  307). 

(2)  Water   roots. — If    a    stem   is    floating,    clusters    of 
whitisli  thread-like  rootlets  usually  put  out  from  it  and 
dangle  in  the  water.     Plants  which  ordinarily  develop  soil 
roots,  if  brought  into  proper  water  relations,  may  develop 
water  roots.     For  instance,  willows  or  other  stream-bank 
plants  may  be  so  close  to  the  water  that  some  of  the  root 
system  enters  it.     In  such  cases  the  numerous  clustered 
roots  show  their  water  character.     Sometimes  root  systems 
developing  in  the  soil  may  enter  tile  drains,  when  water 
roots  will  develop  in  such  clusters  as  to  choke  the  drains. 
The  same  bunching  of  water  roots  may  be  noticed  when  a 
hyacinth  bulb  is  grown  in  a  vessel  of  water.     It  is  evident 


ROOTS 


81 


that  contact  with  abundant  water  modifies  the  formation 
of  roots,  both  as  to  number  and  character. 


(3)  Clinging  roots. — Such  roots  are  developed  to  fasten 
the  plant  body  to  some  support,  and  may  be  regarded  as 


A  TEXT-BOOK  OF  BOTANY 


roots   serving   as   tendrils.      In   the   trumpet-creeper   and 
poison-ivy  these  tendril-like  roots  cling  to  various  supports, 

such  as  stone  walls 
and  tree  trunks, 
by  sending  minute 
branches  into  the 
crevices.  In  such 
cases,  however,  the 
plant  has  also  true 
soil  roots. 

(4)  Air  roots. — 
Some  plants  have  no 
soil  connection  at  alL 
In  the  rainy  tropics,, 
where  it  is  possible 
to  obtain  sufficient 
moisture  from  the 
air,  there  are  many 
such  plants,  notable 
among  which  are  the 
orchids,  to  be  ob- 
served in  almost 
any  greenhouse. 
Clinging  to  the 
trunks  of  trees,  usu- 
ally imitated  in  the  greenhouse  by  nests  of  sticks,  they 
send  out  long  roots  which  dangle  in  the  moist  air  (Fig. 
78).  Such  plants  are  called  epiphytes,  the  name  indi- 
cating that  they  perch  upon  other  plants  and  have  no  con- 
nection with  the  soil  (Fig.  79).  A  very  common  epiphyte 
of  our  Southern  States  is  the  common  long  moss  or  black 
moss  (although  it  is  by  no  means  a  moss)  that  hangs  in 
stringy  masses  from  the  branches  of  live-oaks  and  other 
trees  (Fig.  80). 


FIG.  78. — An  orchid  with  aerial  roots. 


FIG.  79. — A  group  of  aerial  plants  (epiphyte^  in  a  tropical  forest. 
— After  KARSTEN  and  Si  IIKNCK. 


FIG.  80. — Live-oaks  covered  with  long  "moss.1 

83 


< 


CHAPTER  V 

GERMINATION   OP   SEEDS 


42.  Introductory. — In  the  preceding  chapters  the  struc- 
ture and  the  work  of  the  three  great  nutritive  organs  (leaf, 
stem,  and  root)  of  the  higher  plants  were  considered.  In 
studying  the  germination  of  seeds,  these  organs  may  be 
observed  assuming  their  various  positions  and  relations,  and 
the  student  may  be  introduced  to  certain  important  facts. 


FIG.  81. — Section  of  bean;  removing  one  cotyledon,  and  showing  the  testa,  the 
remaining  cotyledon,  the  hypocotyl  (its  tip  in  position  to  emerge),  and  the 
plumule. 

Perhaps  the  most  common  seed  used  in  class  study  of  seed 

germination  is  the  garden  bean,  although  other  seeds  should 

be  germinated  in  the  laboratory,  and,  when  possible,  studies 

of  germination  should  be  extended  beyond  the  laboratory. 

43.  General  structure  of  the  seed. — It  is  very  common 

to  study  even  the  surface  of  the  seed  in  great  detail,  but 

84 


GERMINATION  OF  SEEDS 


85 


only  such  features  as  have  an  evident  bearing  upon  its 
germination  will  be  considered  here.  The  seed  is  invested 
by  a  hard  coat  (testa),  which  in  some  seeds  is  extremely 
hard,  and  is  evidently  a  protective  structure  during  the 
more  or  less  prolonged  period  of 
rest.  Within  the  testa  the  young 
plantlet  is  packed,  at  this  stage 
called  the  embryo  (Fig.  81).  The 
process  of  germination  is  the 
escape  of  this  plantlet  from  the 
testa.  If  the  embryo  of  the  bean 
be  removed  from  the  testa — better 


FIG.  81a. — Section  of  violet  seed,  showing 
embryo,  endosperm,  and  testa. 


FIG.  82.— Seedling  of  bean: 
A,  embryo  removed  from 
testa;  B,  young  seedling 
showing  hypocotyl,  cotyle- 
dons, and  plumule;  C,  older 
seedling  showing  the  first 
internode  and  leaves  of  the 
stem. — After  GRAY. 


done    after  soaking  in   water   for 

some  time — and  straightened  out, 

it  will  be  found  to  consist  of  three 

distinct    parts    (Fig.    82).     The 

most  conspicuous  of  these  is  the  two  "halves"  of  the  bean, 

which  are  the  seed-leaves  (cotyledons)  gorged  with  reserve 

food.     These  cotyledons  stand  upon  a  minute  stem,  which 

in  the  seed  is  curved  up  against  them,  and  which  is  called 

the  hypocotyl,  a  name  applied  to  the  peculiar  stem  of  an 

embryo.     Between  the  cotyledons,  and  arising  from  the  top 


86  A  TEXT-BOOK  OF  BOTANY 

of  the  hypocotyl  is  a  bud,  called  the  plumule,  from  which 
the  future  leafy  stem  is  to  develop.  In  many  seeds  the 
reserve  food  is  not  stored  in  the  cotyledons,  but  in  a  spe- 
cial tissue  surrounding  the  embryo,  which  in  general  may 
be  called  endosperm.  In  the  violet  seed,  for  example, 
within  the  testa  is  the  endosperm,  and  embedded  in  the 
endosperm  lies  the  embryo  (Fig.  8 la). 

44.  Conditions  for   germination. — The   length   of  time 
seeds  may  retain  their  vitality  varies  with  different  plants. 
In  nature  they  are  expected  to  germinate  in  the  growing 
season  following  their  maturity;  but  many  are  known  to  re- 
tain the  power  of  germination  for  several  years  if  kept  in 
proper  conditions,  chief  among  which,  apparently,  is  dry- 
ness.     The  stories  of  the  germination  of  wheat  and  corn  ob- 
tained from  the  wrappings  of  mummies  have  proved  to  be 
myths. 

The  conditions  required  for  germination  are  abundant 
moisture,  suitable  temperature,  and  a  supply  of  oxygen 
(which  means  access  of  air).  Seeds  vary  greatly  in  the 
amount  of  heat  necessary  for  germination,  as  may  be 
inferred  from  the  fact  that  some  seeds  germinate  in  early 
spring  or  even  on  the  melting  snow-fields  of  alpine  and 
arctic  regions,  while  others  need  the  heat  of  the  tropics. 

45.  Absorption  of  water. — When  a  seed  has  been  placed 
in  the  proper  conditions  for  germination,  the  first  visible 
result  is  its  swelling  through  the  absorption  of  water.     The 
amount  and  force  of  this  swelling  may  be  observed  by  plac- 
ing a  quantity  of  seeds  in  a  tumbler  of  water  and  putting 
various  weights  on  the  mass.     It  is  entirely  clear  also  that 
oxygen  has  been  passing  in,  for  the  seed  gives  off  carbon 
dioxide  and  heat.     That  heat  is  given  off  by  a  germinating 
seed  is  made  very  plain  in  the  process  of  malting,  in  which 
a  large  mass  of  barley  is  put  in  germinating  conditions  in  a 
confined  space,  and  the  combined  heat  from  all  the  seeds 
becomes  very  evident. 


GERMINATION  OF  SEEDS  87 

46.  Respiration. — The  escape  of  carbon  dioxide,  which 
follows  the  taking  in  of  oxygen,  is  the  superficial  indication 
that  the  very  important  process  called  respiration  is  going 
on — a  process  that  is  essential  not  only  to  every  living 
animal  and  plant,  but  also  to  every  living  cell.     Just  what 
happens  in  respiration  is  very  uncertain ;  but  it  involves  a 
series  of  changes  in  the  living  substance  (protoplasm)  itself — 
changes  which  are  made  possible  by  the  presence  of  oxygen, 
and  among  whose  results  are  the  liberation  of  carbon  dioxide 
as  a  waste  product,  and  of  energy  for  plant  work,  such  as 
growth  and  movement.     A  plant,  therefore,  cannot  work 
without  respiration;  and  if  it  cannot  work  it  ceases  to  live. 

The  contrast  between  photosynthesis  (§  14)  and  res- 
piration should  be  kept  distinctly  in  mind,  as  the  former 
process  so  masks  the  latter  in  green  plants  exposed  to  light 
that  the  occurrence  and  the  importance  of  respiration  in 
them  is  not  always  fully  appreciated.  It  was  once  custom- 
ary to  contrast  plants  and  animals  by  stating  that  the  form- 
er take  in  carbon  dioxide  and  give  out  oxygen  (photosyn- 
thesis), and  the  latter  take  in  oxygen  and  give  out  carbon 
dioxide  (respiration).  It  is  evident  that  all  living  things, 
whether  plants  or  animals,  are  dependent  upon  respiration; 
while  green  plants  when  exposed  to  light  can  also  do  the 
work  of  photosynthesis.  The  contrast  between  the  two 
processes  may  be  made  still  more  evident  by  the  following 
statement:  photosynthesis  occurs  only  in  green  cells,  re- 
quires light,  uses  carbon  dioxide,  liberates  oxygen,  makes 
organic  material,  and  accumulates  energy;  while  respiration 
occurs  in  every  living  cell,  does  not  require  light,  uses 
oxygen,  liberates  carbon  dioxide,  uses  organic  material,  and 
liberates  energy. 

47.  Digestion. — Before  any  growth  of  the  embryo  can 
take  place  the  reserve  food  must  be  changed.     Most  fre- 
quently in  seeds  the  storage  form  is  starch,  but  starch  is 
insoluble  and  therefore  cannot  move  out  of  the  cells  in 

7 


88  A  TEXT-BOOK  OF  BOTANY 

which  it  is  stored.  Accordingly  it  must  be  changed  into  a 
soluble  form;  and  this  work  is  commonly  done  by  a  sub- 
stance called  an  enzyme,  which  is  produced  by  the  living 
substance  (protoplasm)  of  the  cell.  There  are  numerous 
enzymes,  which  act  upon  different  substances;  but  the  one 
most  frequently  found  in  seeds  is  that  called  diastase,  which 
has  the  power  of  converting  starch  into  one  of  the  soluble 
sugars.  This  process  of  converting  insoluble  food  into  a 
soluble  form  is  digestion,  and  in  ordinary  seeds  the  starch  is 
digested  and  becomes  sugar.  All  of  this  work  preparatory 
to  growth  accounts  for  the  activity  noted  in  the  two  preced- 
ing sections.  The  food  being  in  the  form  of  a  soluble  sugar 
can  leave  the  storage  cells  and  pass  to  the  regions  where 
growth  occurs. 

48.  Assimilation. — In  a  germinating  seed  the  soluble 
sugar  produced  by  digestion  passes  in  solution  from  cell  to 
cell,  according  to  the  laws  of  osmosis,  until  it  reaches  cells 
where  growth  is  taking  place;  that  is,  where  the  protoplasm 
is  forming  new  cells  by  dividing  those  already  formed,  and 
enlarging  the  new  ones  until  each  one  is  as  large  as  the 
cell  of  which  it  was  a  division.     This  cell  division  and  cell 
growth  are  going  on  very  actively  in  the  hypocotyl  and 
plumule  of  the  germinating  seed;  and  when  the  sugar  in 
solution  reaches  the  active  cells,  it  is  used  in  building  up  the 
active   protoplasm,   which  is  being  broken  down  by  its 
activity.     This   transformation  of  food  into  protoplasm, 
by  numerous  intermediate  steps,  is  assimilation. 

49.  Proteids. — Thus  far  we  have  considered  only  carbo- 
hydrate foods,  but  in  building  up  protoplasm  the  carbo- 
hydrates  are   first   used   in   the   manufacture   of   proteids. 
Just  how  proteids  are  formed  is  very  uncertain,  but  they 
are  more  complex  than  carbohydrates;  and  in  addition  to 
the  carbon,  hydrogen,  and  oxygen  of  the  carbohydrates, 
proteids  contain  other  elements,  notable  among  which  are 
nitrogen,  sulphur,  and  phosphorus,  and  these  enter  the 


GERMINATION  OF  SEEDS 


plant  in  various  compounds  found  in  the  soil.  The  white 
of  an  egg  is  an  illustration  of  a  proteid;  and  meat  in  general 
is  a  proteid  food,  as  contrasted  with  bread,  which  is  a  car- 
bohydrate food.  In  many  seeds  proteid  food  is  stored  in  the 
form  of  alcurone  grains.  For  example,  a  section  of  a  wheat 
grain,  or  the  grain  of  any  common  cereal,  shows  aleurone 
grains  in  the  outer  layer  of  endosperm  cells,  just  inside  of  the 
testa;  while  the  other  endosperm  cells  contain  starch  grains. 

50.  Fats. — In  addition  to  carbohydrates  and  proteids, 
some  plants  form  fats,  the  third  kind  of  organic  food;  and 
these  fats  are  sometimes  stored  in  the  seeds  in  liquid  form 
(in  small  drops),  as  in  the  castor-bean,  flaxseed,  etc.     Fats 
contain  carbon,  hydrogen,  and  oxygen  as  do  the  carbo- 
hydrates; but  while  in  the  carbohydrates  the  hydrogen  and 
oxygen  occur  in  the  proportion  of  two  to  one   (H2O),  in 
the  fats  the  proportion  of  oxygen  is  much  less.     In  ad- 
dition to  the  oil  obtained  from  the  seeds  mentioned  above, 
olive  oil  and  cotton-seed  oil  may  be  mentioned  as  plant 
fats  of  commercial  importance. 

51.  Escape   of  the   hypocotyl. — The   first   part   of   the 
seedling  to  push  out  of  the  testa   is  the  tip  of  the  hy- 
pocotyl,    which 

is  to  develop 
the  root.  It 
is  soon  evident 
that  this  elon- 
gating tip  di- 
rects its  growth 
downward,  that 
is,  toward  the 
earth,  even  if 
it  has  to  curve 
about  the  seed 
to  do  so  (Fig. 
83).  It  is  exceedingly 


FIG.  83. — Germinating  beans:  the  bean  to  the  left  has  not 
been  moved;  the  one  to  the  right  was  turned  90°  after 
it  had  reached  the  stage  of  the  other  ' 


sensitive    to    surrounding   influ- 


90  A  TEXT-BOOK  OF  BOTANY 

ences,  a  condition  that  is  called  irritability.  The  outside 
influences  that  affect  irritable  organs  are  called  stimuli; 
for  example,  among  animals  light  is  a  stimulus  to  the 
eye. 

52.  Geotropism. — The  young  root,   developing  at  the 
end  of  the  hypocotyl,  is  very  sensitive  to  gravity,  a  con- 
dition that  is  called  geotropism,  the  root  being  said  to  be 
geotropic.     The  word  means  "directed  by  the  influence  of 
the  earth,"  what  is  commonly  called  gravity  acting  as  a 
stimulus.     If  the  root-tip,  when  it  pushes  out  of  the  testa, 
is    directed    upward    or   horizontally,   gravity   acts   as   a 
stimulus  and  the  irritable  root  responds  by  developing  a 
curvature  that   directs  it  downward   (Fig.   83).     This  is 
only  one  way  of  responding  to  the  stimulus  of  gravity; 
and  since  this  way  directs  the  organ  toward  the  source  of 
the  stimulus,  the  organ  is  said  to  be  positively  geotropic. 
If  the  same  stimulus  and  response  that  directs  the  root-tip 
toward  the  soil   continues  to  direct  it   within  the  soil,  it 
continues-to  grow  directly  downward  and  becomes  a  tap- 
root  (Figs.   68   and  89).     When  such  a  root,  having  en- 
tered the  soil,  begins  to  send  out  branches,  these  do  not 
respond  to  the  stimulus  of  gravity  as  does  the  tap-root, 
for  they  extend  through  the  soil  in  every  direction,  and 
are  evidently  not  positively  geotropic. 

53.  Hydrotropism. — The  root  is  very  sensitive  also  to 
the    presence    of    moisture,    a    condition    that    is    called 
hydrotropism,  the  root  being  said  to  be  hydrotropic.     The 
word  means  "directed  by  the  influence  of  moisture/'  the 
moisture  acting  as  a  stimulus,  and  the  root  being  positively 
hydrotropic.     Since  ordinarily  the  stimuli  of  moisture  and 
gravity  act  from  the  same  general  direction  upon  the  root, 
the   responses   are   not   contradictory.     It   is   of   interest, 
therefore,  to  arrange  an  experiment  that  will  make  them 
contradictory.     An  erect  support,  shaped  as  shown  in  Fig. 
84,  is  covered  with  bibulous  paper  which  is  kept  moist. 


GERMINATION  OF  SEEDS 


91 


To  the  inward  sloping  surface  is  pinned  a  seedling  whose 
root  has  well  started.  The  photograph  (Fig.  84)  shows 
that  the  root,  con- 
tinuing to  grow,  has 
turned  from  the  ver- 
tical direction  under 
the  stimulus  of  the 
moisture  in  the  bibu- 
lous paper,  and  is 
pursuing  a  general  di- 
rection that  is  a  re- 
sultant between  the 
two  stimuli.  A  more 
detailed  observation 
of  such  an  experi- 
ment shows  that  the 
root  -  tip  sometimes 
turns  toward  and 
sometimes  away  from 
the  moist  paper. 

54.  Escape  of  the 
cotyledons  and  the 
plumule. — After  the 
root  with  its  branches 
has  anchored  the 
plantlet  to  the  soil, 
the  hypocotyl  begins  to  elongate  rapidly;  and  since  the 
cotyledons  are  still  within  the  testa  this  elongation  results 
in  the  development  of  an  arch,  the  hypocotyl  arch  (Fig. 
85).  As  the  arch  constantly  seeks  to  straighten  itself,  the 
upward  pull  on  the  cotyledons  finally  draws  them  out  of 
the  testa  and  the  hypocotyl  straightens.  The  cotyledons, 
however,  have  done  their  work,  and  although  they  may 
become  green  and  persist  for  some  time,  in  the  bean  they 
are  of  no  further  importance.  It  is  the  escape  of  the 


FIG.  84. — A  bean  seedling  showing  the  response 
of  the  root  when  the  stimulus  of  gravity  is 
from  one  direction  and  that  of  moisture  from 
another. 


92  A   TEXT-BOOK  OF  BOTANY 

plumule  that  is  especially  significant,  for  it  develops  the 
shoot  (Fig.  85). 


FIG.  85. — A  series  in  the  germination  of  the  garden  bean,  showing  the  hypocotyl 
arch,  the  pulling  out  of  the  cotyledons  and  the  plumule,  and  the  straightening 
of  the  hypocotyl. 

With  the  establishment  of  roots  in  the  soil  and  the 
exposure  of  green  leaves  to  the  light  and  air,  germination 
is  over;  for  the  plant  is  able  to  make  its  own  food. 

55.  Phototropism. — The  stem  is  sensitive  to  the  direc- 
tion of  rays  of  light,  a  condition  that  is  called  phototrop- 


FIG.  86. — A  bean  seedling  that  was  placed  in  a  horizontal  position  and  after  two 
hours  photographed. 

ism,  the   stem  being  said   to  be   phototropic.     The  word 
means  "directed  by  the  influence  of  light,"  the  same  stem 


GERMINATION  OF  SEEDS 


93 


appearing  in  the  word  "photograph."  The  term  helio- 
tropism  is  often  used,  meaning  "directed  by  the  influence 
of  the  sun  ";  but  while  the  sun  is  the  usual  source  of  light, 
it  is  not  the  only  one.  It  should  be  noted  that  it  is  not 
light  in  general  that  acts  as  the  stimulus,  but  the  direction 
of  the  rays  of  light.  The  response 
of  the  stem  to  this  stimulus  is  to 
turn  directly  toward  the  source  of 
the  light  rays;  that  is,  the  stem  is 
positively  phototropic.  Fig/ 86  shows 
a  bean  seedling  that  was  placed  in  a 
horizontal  position  and  two  hours 
afterward  photographed.  Fig.  87 
shows  the  same  plant  completely 
inverted,  allowed  to  grow  for  two 
days,  and  then  photographed.  In 
both  cases  the  strong  curvature 
developed  in  response  to  the  stimu- 
lus of  light  is  very  evident,  the  tip 
of  the  stem  in  both  experiments 
being  directed  toward  the  source 
of  light. 

It  should  be  remembered  that 
these  stimuli  that  influence  direc- 
tion call  forth  a  response  only  when 
the  organ  is  out  of  line,  and  the 
response  or  reaction  is  a  curve  that 
brings  it  back  into  line.  It  is  also 
important  to  note  that  the  sensi- 
tive or  irritable  region  of  an  organ 
is  not  necessarily  the  region  in  which  the  reaction  occurs; 
and  this  means  that  the  stimulus  has  been  transmitted  in 
some  way  from  the  irritable  cells  to  those  that  respond,  for 
example,  by  developing  a  curvature.  Nor  does  the  reac- 
tion follow  the  stimulation  immediately;  for  there  is  an 


FIG.  87.— The  same  seedling 
shown  in  Fig.  86,  com- 
pletely inverted,  and  after 
two  days  photographed. 


94 


A  TEXT-BOOK  OF  BOTANY 


interval,  known  as  reaction  time,  which  is  generally  much 
longer  in  plants  than  in  animals.  The  reaction  time  may 
be  several  hours,  but  the  movement 
of  the  leaves  of  the  sensitive-plant 
(§17)  and  the  snapping  shut  of  the 
leaves  of  Dioncea  (§  20)  follow  the 
stimulation  with  remarkable  prompt- 
ness. 

The  main  stem  in   most    cases   is 
positively  phototropic,  as  shown  before 
(Figs.    86    and    87);    but    it    is    also 
negatively    geotropic.      The    branches, 
jf  -    however,     may     respond     to     these 

FIG.  ss.-A  seedling  of    stimuli  in  a  veIT  different  way,  usu- 
white  mustard  grown  in    ally  extending  in  a  more  or  less  hori- 

water   and   exposed   to  .L    i       j-         j.'  11-  •     i 

weak  light,  showing  the    zontal    direction,    and    being   mainly 


positive    phototropism    transversely    aeotromc. 

of    the    stem    and    the 


The    leaves, 
negative"  phototropism    also,    are    usually    neither    positively 

of  the  root;  the  arrows      nor     negatively     phototropic,    but     are 
indicate  the  direction  of  J      XT 

the  rays  of  light.  directed     horizontally,     being     trans- 


FIG.  89. — A  series  in  the  germination  of  the  scarlet  runner  bean. 


GERMINATION  OF  SEEDS 


95 


FIG.  89«.— First  stage  of  the 
series  shown  in  Fig.  89;  one 
cotyledon  removed  to  show 
the  relation  of  parts,  and  the 
arch  developed  by  the  first 
internode. 

phototropism.  It  is 
interesting  to  note 
that  a  tap-root  be- 
ing positively  geo- 
tropic,  positively  hy- 
drotropic,  and  nega- 
tively phototropic,  all 
of  its  responses  under 
ordinary  conditions 
combine  to  direct  it 
into  the  soil. 

56.  Other  seeds.— 
It  must  not  be  sup- 


versely  phototropic.  The  adjust- 
ment of  the  leaf-blades  to  the 
new  direction  of  the  light  may 
be  seen  in  Fig.  87. 

The  root  also  is  phototropic, 
turning  directly  away  from  the 
source  of  light;  that  is,  it  is 
negatively  phototropic.  Fig.  88 
shows  a  seedling  of  white  mus- 
tard so  arranged  that  both  stem 
and  root  are  exposed  only  to 
weak  light,  the  former  showing 
positive,  the  latter  negative 


FIG.  90. — Seedling  of  castor-bean,  showing  large 
and  green  cotyledons. 


96 


A  TEXT-BOOK  OF  BOTANY 


posed  that  all  of  the  details  of  germination  given  for  the 
garden  bean  are  found  in  the  germination  of  all  seeds.  The 
conditions  for  germination,  and  such  life  processes  as  res- 
piration, digestion,  etc.,  belong  to  the  germination  of  all 
seeds;  but  the  relations  of  parts  to  one  another  and  the 

details  of  the  es- 
cape of  the  young 
plantlet  vary  wide- 
ly, and  should  be 
examined  in  as 
many  plants  as 
possible.  For  ex- 
ample, in  the  scar- 
let-runner bean  the 
cotyledons  are  not 
usually  freed  from 
the  testa,  the  first 
internode  of  the 
stem  developing 
the  arch  and  free- 
ing the  leaves,  as 
may  be  seen  in  the 
series  shown  in 
Figs.  89  and  89a 
which  is  completed 
by  Fig.  57. 

Seeds  such  as 
peas,  castor-bean, 
squash,  and  corn 
also  should  be  ger- 
minated, as  they  show  important  variations.  For  exam- 
ple, in  the  pea  and  the  acorn  the  cotyledons,  so  gorged 
with  food  as  to  have  lost  all  power  of  acting  as  leaves, 
are  never  extricated  from  the  testa;  but  the  plumule  is 
pushed  out  by  the  elongation  of  the  cotyledons  at  their 


FIG.  91. — Seedling  of  corn  at  several  stages,  showing 
the  superficial  position  of  the  embryo,  the  unfold- 
ing leaves,  and  the  roots;  the  single  cotyledon  is 
not  seen,  remaining  in  close  contact  with  the  endo- 
sperm. 


GERMINATION  OF  SEEDS  97 

bases  into  short  or  sometimes  long  stalks.  In  the  castor- 
bean  and  the  squash,  the  cotyledons  not  only  escape  from 
the  testa,  but  become  green  and  work  like  ordinary  leaves 
(Fig.  90). 

In  corn,  as  in  all  the  cereals,  the  embryo  lies  close  against 
one  side  of  the  seed  so  that  it  is  completely  exposed  by  the 
splitting  of  the  thin  skin  that  covers  it.  In  this  case  the 
single  cotyledon  is  never  freely  expanded,  but  remains  as 
an  absorbing  organ  in  contact  with  the  starch-containing 
endosperm,  while  the  root  grows  in  one  direction,  and  the 
stem,  with  its  succession  of  unsheathing  leaves,  grows  in  the 
other  direction  (Fig.  91). 


CHAPTER  VI 


57.  General  characters.  —  Algae  are  the  simplest  green 
plants,  and  it  is  thought  that  the  higher  plants  have  been 
derived  from  them.     They  grow  in  the  water,  and  hence 
their  habits  are  adapted  to  a  water  environment.     They  are 
often  called  seaweeds,  but  although  they  are  very  abundant 
along  seacoasts  they  are  also  abundant  in  fresh  waters. 
Some  of  them  are  so  small  that  the  individual  bodies  are 
visible  only  under  the  microscope,  and  there  is  every  grada- 
tion in  size  from  this  to  the  bulky  bodies  of  certain  marine 
forms. 

Although  all  Algae  contain  chlorophyll,  and  hence  are 
able  to  make  their  own  food  (§  14),  they  do  not  all  appear 
green;  for  in  many  of  them  the  chlorophyll  is  obscured  by 
other  coloring  matters.  The  four  great  groups  of  Algae  are 
named  from  the  general  color  of  their  bodies,  although 
it  must  be  remembered  that  they  all  contain  chlorophyll, 
which  makes  them  independent.  Some  representatives  of 
each  group  are  selected  for  description,  but  they  or  others 
like  them  must  be  examined  before  any  real  knowledge  of 
them  can  be  obtained. 

1.  BLUE-GREEN  ALG^E  (Cyanophycece) 

58.  Gloeocapsa.  —  These  plants  form  blue-green  or  olive- 
green  patches  on  damp  tree  trunks,  rocks,  walls,  etc.     By 
means  of  the  microscope  these  patches  are  seen  to  be  com- 


ALGJE 


99 


posed  of  multitudes  of  spherical  cells,  each  cell  representing 
a  complete  Gloeocapsa  body.  One  of  the  peculiarities  of  the 
plant  is  that  the  outer  part  of  the  cell 
wall  becomes  mucilaginous,  swells, 
and  forms  a  jelly-like  sheath.  Among 
the  cells  examined  there  will  be  found 
some  that  are  dividing,  a  wall  extend- 
ing across  the  spherical  cell  and  di- 
viding it  into  hemispheres.  Each 
hemisphere  is  a  new  plant  which 


FIG.  92.— Glceocapsa:  show- 
ing single  cells,  and  small 
groups  that  have  been 
formed  by  division  and 
are  held  together  by  the 
enveloping  mucilage. 


grows  as  large  as  the 
parent  cell  .and  then 
divides  in  turn.  The 
mucilaginous  walls  hold 
the  cells  together,  and 
so  they  are  found  in 
groups  of  various  sizes 
(Fig.  92).  This  method 
of  reproduction  by  cell- 
division  is  the  simplest 
kind  of  reproduction. 

>  59.  Nostoc.— These 
plants  occur  in  jelly- 
like  masses  in  damp 
places.  If  the  jelly  be 
examined,  it  will  be 
found  to  contain  em- 
bedded in  it  numerous 


IFic.  93.— 4,  Nostoc:  showing  the  chain-like  fila- 
ment and  a  heterocyst  (a)  ;  B.  Glceotrir/nn: 
showing  mucilage  sheath,  basal  heterocyst. 
and  tapering  apex. 


100  A   TEXT-BOOK  OF  BOTANY 

cells  like  those  of  Glceocapsa,  but  they  are  strung  together 
so  as  to  form  chains  of  varying  lengths  (Fig.  93,  A).  The 
jelly  in  which  these  chains  are  embedded  is  formed  from 
the  cell  walls,  as  in  Glceocapsa,  but  it  is  much  more  abun- 
dant. One  notable  fact  in  Nostoc  is  that  the  cells  of  a  chain 
are  not  all  alike,  for  at  irregular  intervals  there  occur  larger 
colorless  cells,  called  heterocysts  (Fig.  93,  A,  a),  a  name 
which  means  simply  "other  cells."  It  is  observed  that 
when  the  chain  breaks  up  into  fragments,  each  fragment 
is  composed  of  the  cells  between  two  heterocysts.  The 
fragments  wriggle  out  of  the  jelly  matrix  and  start  new 
colonies  or  chains,  each  cell  dividing  to  increase  the  length 
of  the  chain.  A  common  plant  related  to  Nostoc  shows 
still  more  differentiation  in  the  cells  of  the  filament,  the 
heterocyst  being  at  the  base,  and  the  end  cells  forming  a 
tapering  and  sometimes  whip-like  termination  (Fig.  93,  B). 

That  each  cell  of  Nostoc  is  an  individual  is  evident  from 
the  fact  that  a  single  cell  separated  from  the  chain  continues 
to  live  and  divides;  and  therefore  the  chain  is  a  colony  of 
individuals,  each  one  reproducing  by  cell-division. 

60.  Oscillatoria. — These  plants  are  found  as  bluish- 
green  slippery  masses  on  wet  rocks,  or  on  damp  soil,  or  freely 
floating.  They  are  simple  filaments  composed  of  very 
short  flattened  cells  (Fig.  94),  and  the  name  refers  to  the 
fact  that  the  filaments  exhibit  a  peculiar  oscillating  move- 
ment. A  filament  is  really  a  row  of  independent  cells 
packed  in  a  mucilaginous  sheath,  like  coins  in  a  coin-case. 
The  cells  are  evidently  flattened  by  mutual  pressure,  for 
the  free  face  of  the  terminal  cell  is  rounded  (Fig.  94,  B); 
and  if  a  filament  is  broken,  and  a  new  cell  surface  exposed, 
it  at  once  bulges  out.  If  a  single  cell  of  the  filament  is 
free  from  all  the  rest,  both  flattened  faces  become  rounded, 
and  the  cell  becomes  spherical.  It  is  evident  that  pressure 
within  the  cell  distends  the  elastic  wall  whenever  it  is  free. 
Each  cell  is  able  to  divide,  forming  new  cells  and  thus 


101 


lengthening  the  filament,  which  may  break  up  into  frag- 
ments, each  fragment  forming  a  new  filament. 

Although  Oscillatoria  is  regarded  as  a  filamentous  colony 
of  individuals,  the  peculiar  waving  and  gliding  movements 
of  the  filament  show  the  cells  working  to- 
gether. The  transition  from  a  colony  of 
one-celled  independent  individuals  to  an 
individual  of  many  interdependent  cells 
is  insensible  and  indefinite. 

61.  Conclusions. — These  three  forms 
of  blue-green  Algae  will  serve  to  illustrate 
the  general  features  of  the  whole  group. 
The  name  of  the  group  refers  to  the  fact 
that  in  addition  to  the  chlorophyll  the 
cells  contain  a  characteristic  blue  color- 
ing matter  which  does  not  mask  the 
green,  but  combined  with  it  gives  a 
bluish-green  tint  to  the  plants  when 
seen  in  masses.  Not  all  the  blue-green 
Algae  are  bluish-green  in  tint,  however;  for  the  presence 
of  other  substances  may  disguise  it,  and  the  color  may  be 
yellow,  or  brown,  or  even  reddish.  For  example,  the 
largest  of  all  the  blue-green  Algae  has  given  name  to  the 
Red  Sea. 

The  group  is  sometimes  called  the  green  slimes  on  ac- 
count of  the  characteristic  slimy,  mucilaginous  walls.  They 
are  very  simple,  being  one-celled  plants,  the  cells  occurring 
singly  or  in  chains  and  filaments.  The  reproduction  is 
exclusively  by  means  of  cell-division;  and  since  the  cells 
that  divide  are  ordinary  working  cells,  this  method  of  re- 
production is  usually  called  vegetative  multiplication.  In 
plants  whose  bodies  are  many-celled,  cell-division  usually 
results  in  the  growth  of  the  individual  rather  than  in  the 
formation  of  new  individuals.  The  power  of  motion  is 
*  marked  in  certain  forms,  and  there  is  also  a  tendency 


Fio.  94.—  Oscillatoria: 

A,  group  of  filaments; 

B,  a  single  filament 
more  enlarged. 


102  A  TEXT-BOOK  OF  BOTANY 

shown  by  the  cells  of  a  colony  to  work  together.  Different 
forms  of  cells  are  exhibited  by  Nostoc  ;  and  this  condition, 
spoken  of  as  the  differentiation  of  cells,  implies  also  a  differ- 
entiation of  work. 

62.  Presence  in  water  reservoirs. — Until  recently  the 
Algae  were  thought  to  be  of  no  importance  to  man;  but  it  is 
now  known  that  the  offensive  odor  and  taste  too  often 
observed  in  drinking  water  are  due  almost  entirely  to  them, 
and  chief  among  the  polluting  forms  are  the  blue-green 
Algae.  This  pollution  of  water  becomes  very  conspicuous 
when  it  occurs  in  city  reservoirs  or  in  ponds,  and  various 
methods  of  purification  have  been  suggested.  Of  these 
none  had  proved  satisfactory,  until  in  1904  the  Department 
of  Agriculture  at  Washington  announced  that  an  effective 
method  of  destroying  the  Algae  or  preventing  their  appear- 
ance had  been  discovered.  It  consists  in  introducing  into 
the  water  a  solution  of  copper  sulphate  so  dilute  that  it  is 
tasteless  and  harmless  to  man;  but  the  warning  is  given  that 
each  reservoir  or  pond  must  be  studied  before  the  proper 
amount  of  the  solution  can  be  known. 


2.  GREEN  ALG.E  (Chlorophyceoe) 

V 

63.  Pleurococcus. — These  plants  are  exceedingly  com- 
mon, occurring  in  masses,  especially  on  the  north  side  of 
tree  trunks,  old  fences,  etc.,  and  looking  like  a  green  stain. 
After  a  few  damp  days  the  green  of  the  masses  becomes 
more  vivid  and  noticeable.  These  finely  granular  green 
masses  are  found  to  consist  of  multitudes  of  spherical  cells, 
resembling  those  of  Gloeocapsa,  except  that  there  is  no  blue 
with  the  chlorophyll,  and  the  cells  are  not  embedded  in  a 
jelly-like  substance  derived  from  the  walls. 

The  cells  may  be  solitary,  or  they  may  cling  together  in 
groups  of  various  sizes  (Fig.  95).  Cells  that  have  just 
divided  may  be  observed  easily,  the  evidence  being  that  the 


ALG^E 


103 


two  daughter  cells  have  not  yet  rounded  off  or  separated, 
so  that  they  appear  as  two  halves  of  the  parent  cell.  Even 
before  they  sepa- 
rate they  may  di- 
vide again,  and 
thus  a  group  of 
cells  may  be 
formed.  Pleuro- 
coccus, therefore, 
is  another  illustra- 
tion of  an  extreme- 
ly simple  plant,  in 
that  it  consists  of 
one  cell  and  repro-  Flo>  ^•—pleurococcui:  A>  *h«  adult  plant,  with  its 

nucleus ;   B-E,  various  stages  of  division  in  pro- 

duceS^by  Cell;jdiyi- ducing  new  cells;    F,  colonies  of  cells  that  have 

'ned  in  contact. 


It  woiilcLea-^e^imagine  a  simpler  plant,  and  the 
pTanTTdngdom  can  be  thought  of  as  beginning  with  individ- 
uals consisting  of  one  green  cell  and  reproducing  by  divi- 
sion. This  one  cell,  however,  absorbs  material,  makes  food, 
assimilates  it,  conducts  respiration,  etc.;  in  fact,  does  all  the 
work  of  living  carried  on  by  plants  with  roots,  stems,  and 
leaves,  although  they  may  contain  millions  of  cells. 

64.  The  plant  cell. — Pleurococcus  may  be  used  to  illus- 
trate the  conspicuous  features  of  a  living  plant  cell.  Bound- 
ing the  cell  there  is  a  thin,  elastic  cell-wall,  composed  of  a 
substance  called  cellulose.  The  cell- wall,  therefore,  con- 
stitutes a  delicate  sac,  which  contains  the  living  substance 
known  as  protoplasm.  It  is  the  protoplasm  that  has  formed 
the  wall  about  itself,  in  the  same  sense  that  a  snail  deposits 
the  shell  about  its  body.  The  protoplasm  is  organized  into 
various  structures  which  are  called  organs  of  the  cell.  One 
of  the  most  conspicuous  protoplasmic  organs  is  the  nucleus, 
a  comparatively  compact  and  usually  spherical  body,  and 
generally  centrally  placed  within  the  cell  (Fig.  95,  A). 


104 


A  TEXT-BOOK   OF  BOTANY 


C' 


In  the  great  majority  of  cells  there  is  a  single  nucleus,  and 
all  about  it,  filling  the  general  cavity  within  the  cell- wall, 
is  a  mass  of  much  less  dense  protoplasm,  known  as  cytoplasm. 
The  cytoplasm  seems  to  form  the  general  background  or 
matrix  of  the  cell,  and  the  nucleus  lies  embedded  within  it. 

Another  protoplasmic  organ  of 
the  cell  is  the  plastid.  Plastids 
are  relatively  compact  bodies, 
and  variable  in  form  and  num- 
ber. The  most  common  kind  of 
plastid  is  the  one  that  contains 
chlorophyll,  and  hence  is  known 
as  the  chloroplastid  or  chloroplast. 
An  ordinary  cell  of  an  alga, 
therefore,  consists  of  a  cell-wall, 
within  which  the  protoplasm  is 
organized  into  cytoplasm,  nu- 
cleus, and  chloroplasts.  With 
proper  staining  the  nucleus  and 
the  chloroplasts  of  Pleurococcus 
can  be  seen;  but  these  structures 

may  be  seen  more  distinctly  and  with  much  less  trouble 
in  the  cells  of  a  moss  leaf  (Fig.  96). 

The  cell-wall  is  elastic,  so  that  the  cell  can  be  compressed 
or  inflated.  The  single  cell  of  Pleurococcus,  unless  pressed 
upon  by  neighboring  cells,  retains  a  spherical  form  as  long 
as  it  is  alive,  a  fact  which  shows  that  there  is  constant  and 
uniform  pressure  on  the  wall  from,  within  the  cell.  It  is 
found  that  this  pressure  is  due  to  the  absorption  of  water 
in  sufficient  amount  to  stretch  the  wall,  this  distended  con- 
dition of  the  cell  being  called  turgor,  a  name  indicating 
that  the  cell  is  turgid.  Pleurococcus  retains  its  spherical 
form, 4'heref ore,  because  it  is  turgid;  and  the  bulging  of 
free  walls  of  Oscillatoria  (§  60)  is  due  to  the  turgor  of 
the  cells. 


FIG.  96.— Cells  of  a  moss  leaf,  show- 
ing chloroplasts  (a),  nucleus  (6), 
and  cytoplasm  (c). 


105 


65.  Ulothrix. — These  are  bright  green,  thread-like 
plants  found  in  the  shallow,  moving  water  of  streams  or 
lake  margins,  where  they  are  anchored  to  sticks  or  stones. 
Each  plant  is  a  simple  (unbranched)  filament,  composed  of 
a  single  row  of  cells;  and  the  cells  are  all  alike  excepting 
that  the  lowest  one  is  usually  colorless,  and  is  elongated 
and  more  or  less  modified  to  act  as  a  holdfast,  anchoring 
the  filament  to  its  support  (Fig.  97,  A).  With  the  possi- 


FIG.  97. — Ulothrix:  A,  base  of  filament,  showing  holdfast  cell  and  five  vegetative 
cells,  each  with  a  single  conspicuous  cylindrical  chloroplast  (seen  in  section) 
surrounding  a  nucleus;  B,  four  cells  containing  swimming  spores;  C,  one  cell 
containing  four  swimming  spores  (a),  a  free  swimming  spore  (6),  a  cell  (c)  from 
which  most  of  the  gametes  have  escaped,  pairing  gametes  (rf),  and  the  resulting 
oospores  (e);  D,  young  filament  from  a  swimming  spore;  E,  oospore  growing 
after  rest;  F,  oospore  producing  swimming  spores. — E  and  F,  after  DODEL-PORT. 

ble  exception  of  the  holdfast  cell,  in  each  cell  there  may  be 
seen  a  nucleus  and  a  single  chloroplast  of  peculiaAMrn, 
being  a  thick  cylinder  investing  the  rest  of  the  cell-conBits. 
As  seen  under  the  microscope  in  optical  section,  thej^lin- 


106  A  TEXT-BOOK  OF  BOTANY 

drical  chloroplast  appears  as  a  thick  green  mass  on  each 
side  of  the  central  nucleus  (Fig.  97,  A).  Each  cell  is  able 
to  divide,  and  so  the  filament  grows  in  length;  or  frag- 
ments of  old  filaments  may  develop  new  ones,  resulting  in 
vegetative  multiplication. 

Although  each  cell  of  the  filament  is  an  ordinary  nutri- 
tive cell,  under  certain  conditions  one  or  more  of  these  cells 
contain  other  cells,  that  have  been  formed  by  what  is  called 
the  internal  division  of  the  older  one  (Fig.  97,  B).  In 
ordinary  cell-division  the  wall  of  the  old  cell  forms  a  part 
of  the  walls  of  the  two  new  cells;  but  in  internal  division 
the  wall  of  the  old  cell  is  only  a  case  which  encloses  the  new 
ones,  and  from  which  they  escape.  When  these  cells  formed 
by  internal  division  escape  from  the  mother-cell  into  the 
water,  it  is  discovered  that  they  are  able  to  swim  about  by 
the  lashing  movements  of  four  cilia  that  appear  in  a  cluster 
at  the  pointed  end  (Fig.  97,  C,  b).  After  a  time  these 
swimming  cells  settle  down,  lose  their  cilia,  and  by  division 
begin  the  development  of  new  filaments  like  those  from 
which  they  came  (Fig.  97,  D).  It  is  evident  that  the 
swimming  cells  have  introduced  a  new  method  of  reproduc- 
tion— a  method  that  involves  the  formation  of  a  special  cell 
for  reproduction,  quite  distinct  from  the  ordinary  nutritive 
cells.  A  special  cell  thus  set  apart  for  reproduction  is  called 
a  spore,  and  spores  that  swim  are  distinguished  as  swim- 
ming spores.  A  very  important  fact  about  Ulothrix,  there- 
fore, is  that  it  reproduces  not  only  by  vegetative  multipli- 
cation, but  also  by  swimming  spores. 

In  other  cells  of  the  same  filaments,  or  in  cells  of  fila- 
ments under  different  conditions,  the  same  formation  of 
cells  by  internal  division  may  be  observed;  but  the  con- 
tained cells  are  smaller  and  more  numerous  (Fig.  97,  C,  c). 
When  they  escape,  it  is  discovered  that  they  also  are  ciliated 
swimming  cells;  but  since  they  do  not  produce  new  fila- 
ments, it  is  evident  that  they  are  not  swimming  spores. 


ALG.E  107 

It  has  been  observed  that  these  small  swimming  cells  come 
together  in  pairs  and  fuse  (Fig.  97,  C,  d),  each  pair  thus 
forming  one  new  cell  (Fig.  97,  C,  e).  The  cell  thus  formed 
passes  through  a  resting  period  (usually  during  winter), 
then  begins  to  grow  (Fig.  97,  £),  and  finally  produces  four 
swimming  spores  (Fig. .97,  F),  each  of  which  is  able  to  pro- 
duce a  new  filament  of  Ulothrix.  Here  is  evidently  a  third 
method  of  reproduction,  which  is  peculiar  in  the  fact  that 
two  special  cells  unite  to  form  the  spore  that  produces  the 
new  plant.  These  two  special  cells  are  gametes  (sexual 
cells);  their  act  of  fusion  is  fertilization;  the  spore  thus 
formed  is  the  oospore  (egg-spore);  and  this  kind  of  re- 
production is  called  sexual  reproduction.*  It  should  be 
observed  that  the  swimming  spores  and  the  oospores  of 
Ulothrix  do  not  differ  in  what  they  are  able  to  do,  but  in 
the  method  of  their  formation,  one  being  formed  by  cell- 
division  and  the  other  by  cell-fusion;  but  to  distinguish  re- 
production by  spores  from  sexual  reproduction  by  oospores, 
the  former  is  called  asexual  reproduction,  and  the  spores  are 
often  spoken  of  as  asexual  spores;  although  when  the  word 
"spore "is  used  it  generally  implies  an  asexual  spore. 

The  three  methods  of  reproduction  found  in   Ulothrix 
may  be  summarized  in  the  following  graphic  way: 

(1)  Vegetative  multiplication  is  indicated  by  P — P — 
P — P — ,  in  which  P  stands  for  the  plant,  there  being  a 
succession    of   plants    arising  directly  one  from  the  other 
without  the  interposition  of  any  special  cells. 

(2)  Reproduction   by   asexual   spores  is  indicated   by 
P — o — P — o — P — o — P — ,  indicating  that  new  plants  are 
not  produced  directly  from  the  old  ones,  but  that  between 
the  successive  generations  there  is  the  asexual  spore. 


*  It  does  not  seem  wise  to  multiply  terms  at  this  point,  and  hence 
the  more  general  terms  "fertilization"  and  "oospore"  are  used  as  in- 
cluding the  more  special  terms  "conjugation"  and  "zygospore." 


108 


A  TEXT-BOOK  OF  BOTANY 


(3)  Sexual  reproduction  is  indicated  by 

>-Mi:>Hl>-^ 
indicating  that  two  special  cells  (gametes)  are  produced  by 
the  plant,  that  these  two  fuse  to  form  one  (oospore) ,  which 
then  produces  a  new  plant. 

66.  Cladophora.— This  plant  is  found  attached  to 
sticks  and  stones  at  the  edge  of  ponds  or  lakes,  and  is  often 

so  abundant  as  to  form  thick 
mats  of  long  anchored  filaments. 
It  is  easily  distinguished  from 
Ulothrix,  for  it  is  a  much  coarser 
plant  and  branches  freely  (Fig. 
98).  It  is  mentioned  here  both 
because  it  is  common  and  be- 
cause it  illustrates  a  branching 
filamentous  body.  Just  as  in 
Ulothrix,  reproduction  in  Clado- 
phora is  carried  on  by  means  of 
swimming  spores,  and  also  by 
the  fusion  of  swimming  gametes 
to  form  oospores. 

67.  CEdogonium.  —  The  fila- 
ments of  CEdogonium  are  long 
and  simple,  the  lowest  cell  act- 
ing as  a  holdfast,  as  in  Ulothrix 
and  Cladophora.  In  each  cell  a  nucleus  may  be  seen  (Fig. 
99),  and  apparently  several  chloroplasts;  but  really  there 
is  only  one  large  complex  chloroplast. 

Any  one  of  these  cells  may  produce  within  itself  a  single 
large  swimming  spore,  which  escapes  from  the  mother-cell 
into  the  water  (Fig.  99,  C).  At  its  more  pointed  clear  end 
there  is  a  little  crown  of  cilia,  by  means  of  which  it  swims 
about  rapidly.  These  spores  finally  anchor  themselves, 
and  each  one  produces  a  new  filament  (Fig.  99,  D  and  #). 


FIG.  98.— Cladophora:  a  branch- 
ing filament,  each  of  whose 
cells  contains  several  nuclei. 


ALG^E 


109 


Certain  cells  of  the  filament  become  very  different  from 
the  ordinary  cells,  enlarging  and  becoming  globular  (Fig. 
99,  A  and  B).  In  each  one  of  these  spherical  cells  there  is 


FIG.  99.—(Edogonium:  A,  portion  of  filament  showing  vegetative  cell  with  its 
nucleus  (rf).an  oogonium  (a)  filled  by  a  large  egg  packed  with  food,  a  second 
oogonium  (c)  containing  an  oospore,  as  shown  by  heavy  wall,  and  two  antheridia 
(6),  each  containing  two  sperms;  B,  portion  of  filament  showing  antheridia  (a), 
from  which  two  sperms  (6)  have  escaped,  a  vegetative  cell  with  its  nucleus,  and 
an  oogonium  which  a  sperm  has  entered  (c),  and  whose  egg  nucleus  (d)  may  be 
seen;  C,  swimming  spore;  D  and  E,  young  filaments  developing  from  swimming 
spores. 


110  A  TEXT-BOOK  OF  BOTANY 

formed  a  single  large  gamete,  which  remains  in  the  cell  that 
produces  it.  This  large  gamete,  which  remains  passive,  is 
the  female  gamete  or  egg,  and  the  globular  cell  that  produces 
it  is  the  oogonium  (egg-case).  In  the  figure  (Fig.  99,  A 
and  B]  these  large  eggs  are  seen  packed  with  roundish 
masses  of  reserve  food. 

Other  cells,  either  in  the  same  filament  or  in  some  other 
filament,  differ  from  the  ordinary  cells  in  being  much 
shorter  (Fig.  99,  A,  b,  and  B,  a).  In  each  of  them  one  or 
two  gametes  are  formed  and  are  set  free,  swimming  about 
like  small  swimming  spores  (Fig.  99,  B,  6).  These  active 
gametes  are  the  male  gametes  or  sperms,  and  the  short  cell 
that  produces  them  is  the  antheridium. 

The  sperms  swim  actively  about  in  the  vicinity  of  an 
oogonium,  and  sooner  or  later  one  enters  through  an  open- 
ing in  the  oogonium  wall  and  fuses  with  the  egg  (Fig.  99, 
B,  c).  As  a  result  of  this  act  of  fertilization  an  oospore 
is  formed  that  soon  organizes  a  firm  wall  about  itself  (Fig. 
99,  A,  c).  This  firm  wall  indicates  that  the  oospore  is  not 
to  germinate  immediately,  but  is  to  be  protected  through  an 
unfavorable  season,  such  as  failure  of  food  supply,  cold, 
or  drought. 

It  is  evident,  therefore,  that  although  both  the  swimming 
spores  and  the  oospores  are  able  to  produce  new  plants,  the 
former  germinate  immediately  and  enable  the  plant  to 
spread  during  the  growing  season,  while  the  latter  last 
through  the  winter  when  the  parent  plants  have  perished, 
and  form  new  plants  in  the  new  growing  season. 

The  most  important  fact  illustrated  by  (Edogonium  is 
that  the  gametes  are  not  alike,  as  in  Ulothrix  and  Clad- 
ophora,  but  have  become  very  unlike.  One  of  them  (the 
egg)  is  relatively  large  and  passive;  the  other  (the  sperm) 
is  relatively  small  and  active.  In  this  case,  therefore,  the 
two  sexes  are  apparent,  and  we  recognize  male  and  female 
gametes. 


111 


68.  Vaucheria. — This  is  one  of  the  most  common  of  the 
green  Algae,  occurring  in  felt-like  masses  of  coarse  filaments 

in  shallow  water  and  on 
muddy  banks,  and  also 
commonly  found  on  the 
damp  earth  and  pots  of 
greenhouses.  It  is  often 
called  green  felt.  The 
filament  is  very  long  and 
usually  branches  exten- 
sively; but  its  great  pe- 
culiarity is  that  there  is 


FIG.  100. — Vaucheria:  showing 
the  large,  branching,  cceno- 
cytic,  filamentous  body,  con- 
taining numerous  chloro- 
plasts  and  nuclei. 

no  partition  wall  in 
the  whole  body,  which 
forms  one  long  con- 
tinuous cavity.  This 
cavity  is  full  of  cyto- 
plasm, and  embedded 
in  the  cytoplasm  are 
very  numerous  chloro- 
plasts  and  also  numer- 
ous nuclei  (Fig.  100). 
Such  a  body,  contain- 
ing nuclei  not  sepa- 
rated from  each  other 
by  cell-walls,  is  called  a  cwnocyte  (common  cell),  or  it  is 
said  to  be  ccenocytic. 


FIG.  101. — Vaucheria:  showing  the  formation 
of  the  lirge  spore  (A),  its  discharge  (B),  and 
the  beginning  of  a  new  filament  (C). 


112 


A  TEXT-BOOK  OF  BOTANY 


Vaucheria  produces  very  large  asexual  spores.  The 
tip  of  a  branch  becomes  separated  from  the  rest  of  the  body 
by  a  wall  (Fig.  101,  A).  In  this  improvised  chamber  the 
whole  of  the  contents  form  a  single  large  spore.  It  escapes 
into  the  water  through  an  opening  in  the  wall,  (Fig.  101,  B) 
and  finally  develops  a  new  filament  (Fig.  101,  C). 

Sex  organs  (antheridia  and  oogonia)  are  also  developed. 
In  a  common  form  of  Vaucheria  they  appear  separately  on 
the  side  of  the  large  coenocytic  body,  and  are  separated 
from  the  general  cavity  by  walls.  The  oogonium  is  a 
globular  cell  (Fig.  102,  6),  usually  with  a  perforated  beak 
for  the  entrance  of  sperms  (Fig.  102,  /),  and  contains  a  single 


FIG.  102. — Sexual  reproduction  in  Vaucheria:  A,  a  single  antheridial  branch  with 
an  empty  antheridium  (a)  at  its  tip,  and  also  an  oogonium  (6)  containing  a 
heavy-walled  oospore  (c)  and  showing  the  beak  (/)  through  which  the  sperm 
passed;  B,  another  species,  in  which  a  single  branch  bears  several  oogonia,  and 
a  terminal  coiled  antheridium. 

large  egg.  The  antheridium  is  a  much  smaller  cell,  on  the 
end  of  a  branch  (Fig.  102,  a),  within  which  numerous  very 
small  sperms  are  formed.  The  usual  escape  into  the  water 
and  entrance  into  the  oogonium  is  followed  by  fertilization 
(one  sperm  fusing  with  the  egg),  which  results  in  an  oospore. 
The  oospore  develops  a  thick  wall  and  is  thus  protected  until 
the  next  growing  season  (Fig.  102,  c).  In  another  species, 


ALGLE 


113 


often  more  abundant,  a  single  branch  from  the  main  body 
bears  several  lateral  oogonia  and  a  terminal  coiled  anther- 
idium  (Fig.  102,  B). 

The  two  important  facts  illustrated  by  Vaucheria  are 
the  coenocytic  body  and  the  development  of  special  cells  to 
act  as  sex  organs. 


FIG.  103. — Spirogyra:  one  complete  cell,  showing  the  spiral,  band-like  chloroplasts, 
with  embedded  pyrenoids,  and  a  nucleus  (near  the  center)  swung  by  radiating 
strands  of  cytoplasm. 

*  69.  Spirogyra.— 
This  is  one  of  the  most 
common  of  the  pond 
scums,  occurring  in 
slippery  and  often 
frothy  masses  of  deli- 
cate filaments  floating 
in  still  water  or  about 
springs.  The  filaments 
are  simple,  and  are  not 
anchored  by  a  special 
basal  cell. 

The  cells  contain  re- 
markable chloroplasts, 
which  are  bands  pass- 
ing spirally  about  with- 
in the  cell-wall  (Figs. 
103  and  104).  These 
bands  may  be  solitary 

Or  Several  in  a  Cell,  and      FlG-  104.— Sptnw/ra:  A-C,  various  stages  in  the 

development  of  sexual  tubes;  D,  a  completed 

form  very  striking  and 


114 


A   TEXT-BOOK  OF  BOTANY 


conspicuous  objects.  The  band  is  not  flat,  and  to  deter- 
mine its  form  is  an  excellent  exercise  for  a  student  learn- 
ing to  reconstruct  objects  under  the  microscope.  Embed- 
ded in  the  chlorophyll  band  nodule-like  bodies  (pyrenoids) 
are  seen,  around  which  a  granular  zone  of  starch  grains  is 
often  visible.  In  favorable  material,  notably  cells  with  a 
single  band,  the  nucleus  may  be  seen,  surrounded  by  a  zone 
of  cytoplasm  that  is  connected  by  radiating  strands  with 
the  cytoplasm  against  the  wall  (Fig.  103). 

Spirogyra  is  peculiar  in  producing  no  swimming  spores, 
or  asexual  spores  of  any  kind.     Its  method  of  sexual  re- 


FIG.  105. — Spirogyra,  showing  some  common  exceptions:  A ,  two  connected  cells- 
that  have  formed  oospores  without  fusion,  and  a  second  cell  that  has  attempted 
to  connect  with  one  of  them;  B,  cells  of  three  filaments,  the  cells  of  the  cen- 
tral one  having  connected  with  both  the  others. 

production  also  is  peculiar.  Cells  of  two  adjacent  fila- 
ments put  out  protuberances  toward  one  another;  and  where 
they  come  in  contact  an  opening  is  formed,  the  result  being 
that  there  is  a  continuous  passageway  connecting  a  cell  of 
one  filament  with  a  cell  of  the  other  (Figs.  104  and  105). 
When  many  of  the  cells  of  two  parallel  filaments  become 
thus  united,  the  appearance  is  that  of  a  ladder,  with  the 
filaments  as  the  side  pieces  and  the  connecting  tubes  as  the 


ALGJE 


115 


rounds.  In  each  cell  thus  connected  with  another  a  single 
large  gamete  is  formed,  and  one  of  them  passes  through  the 
connecting  tube  to  the  other.  The  gametes  are  similar,  and 
their  fusion  results  in  a  heavy- walled  oospore  (Fig.  104,  D), 
which  endures  through  the  winter  and  germinates  during 
the  following  season. 

Plasmolysis. — Spirogyra  is  a  very  favorable  form  for 
demonstrating  plasmolysis,  which  means  the  shrinkage  of 
protoplasm  from  loss  of 
water.  The  cytoplasm 
of  an  active  cell  is  full  of 
water,  which  often  col- 
lects in  droplets  of  vary- 
ing size,  called  vacuoles.  - 
There  is  always  a  layer 
of  cytoplasm  in  close  con-  B 
tact  with  the  cell-wall, 
but  the  interior  of  the 
cell  may  be  one  large 
vacuole  traversed  by 
strands  of  cytoplasm,  as 
in  Spirogyra.  The  turgor  of  the  cell  (§  64)  keeps  the  elastic 
wall  distended;  but  if  the  cell  be  put  in  a  solution  of  sugar, 
water  will  be  withdrawn.  The  vacuoles  thus  beginning 
to  lose  their  water,  the  cytoplasm  shrinks;  and  if  the  loss 
continues,  the  vacuoles  are  obliterated,  and  the  layer  of 
cytoplasm  in  contact  with  the  wall  separates  from  it,  all 
the  cytoplasm  of  the  cell  contracting  into  a  compact  mass 
(Fig.  106).  The  name  plasmolysis  really  means  the  "  loosen- 
ing" of  the  "plasma"  (protoplasm)  from  the  wall.  Any- 
thing that  withdraws  water  from  a  cell  plasmolyzes  it,  and 
the  filamentous  Algae  are  favorable  forms  for  experiments 
to  show  this. 

70.  Conclusions. — The  green  Algae  are  so  named  because 
the  green  of  the  chloroplasts  is  neither  modified  nor  obscured 


FIG.  106. — Plasmolysis:  A,  a  cell  of  Spirogyra 
before  plasmolysis;  B,  the  same  cell  after 
plasmolysis  with  a  ten  per  cent  solution  of 
salt. 


116  A  TEXT-BOOK  OF  BOTANY 

by  other  colors,  and  tne  plants  have  a  characteristic  grass- 
green  color.  As  indicated  by  the  illustrations  given  above, 
they  include  simple  one-celled  forms  which  reproduce  only 
by  cell-division  (vegetative  multiplication),  .and  simple 
or  branching  filamentous  forms  which  also  reproduce  by 
swimming  spores  and  cospores.  Such  filamentous  forms 
as  Ulothrix,  Cladophora,  and  (Edogonium  are  representa- 
tives of  a  group  known  as  the  Conferva  forms,  having 
bodies  of  many  cells  and  swimming  spores.  Vaucheria 
represents  the  large  group  of  Siphon  forms,  characterized 
by  their  crenocytic  bodies.  Spirogyra  represents  the  Con- 
jugate forms,  the  name  meaning  "yoked  together,"  and 
referring  to  the  connecting  of  the  filaments  for  fertilization; 
the  group  is  characterized  also  by  the  absence  of  swimming 
spores  and  the  peculiar  chloroplasts,  not  all  of  which  are 
spiral  bands. 

The  bodies  of  green  Algae  are  not  all  single  cells  or 
filaments,  the  marine  sea-lettuces,  belonging  with  the 
Conferva  forms,  having  broad,  flat,  leaf-like  bodies  that 
have  suggested  the  common  name.  Some  of  the  green 
Algae  are  associated  with  the  blue-green  Algae  in  the  pol- 
lution of  water  reservoirs  referred  to  in  §  62. 

3.  BROWN  ALG.E  (Phceophycece). 

71.  General  characters. — The  two  preceding  groups  are 
the  most  common  Algae  of  the  fresh  waters,  but  the  brown 
Algae  are  almost  all  of  them  marine.  The  association  of  a 
brown  coloring  matter  with  the  chlorophyll  has  given  name 
to  the  group,  and  the  plant  bodies  display  various  shades  of 
yellow,  brown,  or  olive.  In  size  the  brown  Algae  range 
from  forms  that  are  microscopic  to  those  that  are  hundreds 
of  feet  long.  They  belong  chiefly  to  the  colder  waters  of 
the  globe,  reaching  their  greatest  development  in  the  arctic 
and  antarctic  regions.  The  greatest  displays  of  huge  bodies 


117 


along  our  own  coasts  are  to  be  found  on  the  rocky  shores  of 
the  North  Atlantic  and  the  North  Pacific,  the  display  on 
the  latter  coast  being  especially  rich  in  forms.  They  are 
all  anchored  plants,  the  strong  holdfasts  and  leathery  bodies 
enabling  them  to  live  exposed  to  strong  waves  and  cur- 
rents. 

The  largest  forms  are  the  kelps  (Laminarias),  the  general 
habit  of  body  being  a  stem  fastened  to  the  rocks  by  a  cluster 


FIG.  107.— A  common  kelp,  showing  root- 
like  holdfast,  stalk,  and  blade. — Alter 
SAUNDERS. 


of  strong,  root-like  holdfasts,  and  ending  in  a  blade-like 
expansion  (Fig.  107).  The  giant  kelps  of  the  Pacific  Coast 
are  the  most  notable  forms.  One  of  these  has  a  stem  about 


FIG.  108. — A  kelp  with  very  long  and  rope- 
like  stem  bearing  numerous  leaves. — 
After  BENNETT  and  MURRAY. 


as  large  as  a  clothes-line,  reported  as  sometimes  reaching  a 
length  of  900  feet,  and  bearing  numerous  leaves  (Fig.  108). 
The  bladder  kelp  has  a  very  long  flexible  stem  (120  to  150 


us 


A  TEXT-BOOK  OF  BOTANY 


feet)  that  swells  at  the  end  into  a  large  globular  float,  to 
which  are  attached  leaves  often  ten  or  twelve  feet  long 
(Fig.  109).  The  sea-palm  has  a  thick  erect  stem  that  bears 
a  crown  of  large  drooping  leaves  (Fig.  110). 


FlG.  109. — A  bladder  kelp. — After  POSTELS  and  RUPRECHT. 

Another  group  of  brown  Algae  is  represented  .by  the  rock- 
weeds  (called  also  wrack)  and  the  gulfweeds.  The  former 
(mostly  Fucus)  cover  the  rocks  between  tide-marks,  being 
ribbon-like  forms  repeatedly  forking  at  the  swollen  tips 


ALG.E  119 

and  often  bearing  air-bladders  to  assist  in  floating  (Fig. 

111).  The  most  complex  body  is  that  of  the  gulf  weed 

(Sargassum),  in  which  there 
are  slender  branching  sterna 


FIG.    110.  —  A    sea-palm.  —  After   Ru-         Fio.  111. — Fragment  of  Fucut,  showing 

PRECHT.  forked  branching,  reproductive  tips, 

and  air-bladders. — After  LUERSSEN. 

bearing  numerous  leaves  like  ordinary  foliage,  and  stalked 
air-bladders  that  resemble  berries  (Fig.  112).  The  gulf- 
weeds  occur  in  warmer  waters  than  do  the  other  large  forms, 
and  are  often  torn  from  their  anchorage  and  carried  away 
from  the  coast  by  currents,  collecting  in  the  great  sea  eddies 
produced  by  oceanic  currents  and  forming  the  so-called 
Sargasso  seas.  Some  of  the  gulfweeds  forming  these  masses 

9 


120  A  TEXT-BOOK  OF  BOTANY 

of  vegetation  floating  in  mid-ocean  continue  to  grow  luxu- 
riantly, especially  in  warmer  parts  of  the  Atlantic. 

From  the  ashes  of  kelps  and  rockweeds  the  chief  supply 
of  iodine  is  obtained;  and  these  great  masses  of  vegetation, 


FIG.  112. — Fragment  of  Sargassum,  showing  differentiation  of  the  thallus  into 
stem-like  and  leaf-like  portions,  and  also  the  bladder-like  floats. — After  BENNETT 
and  MURRAY. 

thrown  up  or  left  exposed  by  the  tides,  are  used  for  enriching 
farm  lands. 

72.  Ectocarpus. — The  two  principal  groups  of  brown 
Algae  are  distinguished  from  each  other  by  their  re- 
production. By  far  the  larger  group  includes  the  kelps, 
whose  method  of  reproduction  is  very  simple,  although  many 


ALG^E 


121 


of  their  bodies  are  huge.  Ectocarpus  may  be  used  to 
illustrate  the  essential  features  of  the  group.  Its  body  is 
filamentous  (Fig.  113),  suggesting  the  body  of  some  of  the 
Conferva  forms  among  the  green  Algae.  Certain 
cells  of  the  filament  (Fig.  113,  A),  or  the  end  cells 
of  special  short  branches,  become  enlarged  and 
produce  numerous  swimming  spores.  The  swim- 
ming spores  of  brown  Algae  are  peculiar  in  usu- 
ally bearing  the  two  cilia  on  one  side  of  the  body 
rather  than  at  one  end,  and  hence 
they  are  described  as  laterally  bicili- 
ate  (Fig.  115,  G). 

The  cell  that  produces  swimming 
spores  was  sometimes  spoken  of 
among  the  green  Algae  as  a  mother- 
cell,  but  a  mother-cell  may  not  al- 
ways produce  spores. 
Hence  it  is  well  to  use  £~ 

a  term  that  implies  the 
product  of  the  mother- 
cell,  and  in  this  case 
the  term  is  sporangium 
(spore-case).  A  sporan- 
gium, therefore,  is  an  or- 
gan that  produces  spores; 
and  among  the  Algae  de- 
scribed thus  far  it  con- 
sists of  one  cell. 

In  addition  to  the  one- 
celled  sporangia,  other 
organs  in  similar  posi- 
tions may  occur;  but 
they  differ  from  the  spo- 
rangia in  being  many-celled  (Fig.  113,  B).  In -each  cell 
usually  one  body  is  formed,  which  when  discharged  is  seen 


B 


FIG.  113. — Ectocarpus:  a  filamentous,  branch- 
ing form:  A.  filament  bearing  one-celled 
sporangia  («);  B,  filament  bearing  many- 
celled  gametangia  (#). 


122 


A  TEXT-BOOK  OF  BOTANY 


to  resemble  the  swimming  spores.  However,  it  fuses  with 
another  cell  of  the  same  kind,  and  this  behavior  and  the 
result  show  that  it  is  a  gamete.  As  a  result  of  this  act  of 
fertilization  an  oospore  is  formed,  as  in  the  case  of  Ulothrix 
(§  65).  This  kind  of  sexual  reproduction  is  regarded  as 
simple  because  the  pairing  gametes  are  alike,  and  have  not 
become  distinguished  as  egg  and  sperm,  as  in  (Edogonium 
(§  67)  and  Vaucheria  (§  68).  In  those  plants  separate 
names  were  given  to  the  organs  producing  eggs  (oogonia) 
and  those  producing  sperms  (antheridia).  In  Ulothrix  and 
Ectocarpus,  on  the  other  hand,  no  such  distinction  can  be 
made,  and  hence  the  organ  producing  gametes  is  called  a 
gametangium  (gamete-case).  Of  course  oogonia  and  an- 
theridia are  gametangia,  but  the  latter  name  is  generally 

used  only  when  the 
gametes  are  alike.  In 
Ectocarpus,  therefore, 
many-celled  gametan- 
gia are  produced  (Fig. 
113,  B),  in  addition  to 
one  -  celled  sporangia 
(Fig.  113,  A). 

This  great  group  of 
brown  Algae,  of  which 
Ectocarpus  is  here  used 
as  a  representative, 
is  distinguished,  there- 
fore, by  its  swimming 
spores  and  its  similar 
gametes. 

73.  Fucus.  — The 
smaller  group  of  brown 
Algae  comprises  the 
rockweeds  (Fucus)  and  the  gulf  weeds  (Sargassum),  the 
former  of  which  may  be  used  to  illustrate  the  group. 


7U- 


FIG.  114. — Fucus:  showing  a  section  of  the  cavity 
(conceptacle)  containing  the  sex-organs,  in 
this  case  only  oogonia. — After  THURETO 


ALG.E 


123 


In  the  swollen  and  forked  tips  (Fig.  Ill)  of  the  rib- 
bon-like body  of  Fucus  numerous  flask-shaped  cavities  oc- 
cur, each  of  which  communicates  with  the  surface  by  a 


FIG.  115. — Fucus:  showing  eggs  in  the  oogonium  (A)  and  after  discharge  (E),  anther- 
idium  containing  sperms  (C),  the  discharged  laterally  biciliate  sperms  (G),aud 
eggs  surrounded  by  swarming  sperms  (F  and  H). — After  STRASBUHGER. 


124:  A  TEXT-BOOK  OF  BOTANY 

small,  pore-like  opening  (Fig.  114).  On  the  walls  of  these 
cavities  oogonia  and  antheridia  are  produced.  The  oogo- 
nium  is  peculiar  in  that  it  usually  produces  eight  eggs, 
which  are  discharged  and  float  free  in  the  water  (Fig.  115, 
A  and  E).  About  these  eggs  the  sperms  swim  in  great 
numbers,  often  striking  against  them  and  setting  them 
rotating  (Fig.  115,  F  and  H).  Finally,  a  single  sperm  fuses 
with  an  egg  and  an  oospore  is  formed,  which  later  produces 
a  new  Fucus  plant. 

This  group  of  brown  Alga3,  therefore,  differs  from  the 
other  one  in  producing  no  swimming  spores,  and  in  its 
dissimilar  gametes  (eggs  and  sperms). 

• 
4.  RED  ALG.E  (Rhodophycece) . 

74.  General  characters. — The  red  Algae  are  mostly 
marine  forms,  and  receive  their  name  from  the  fact  that 


FIG.  116. — One  of  the  red  Algae. 


a  red  coloring   matter  completely  masks  the  chlorophyll. 
As  a  consequence,  the  plants  are  various  shades  of  red, 


ALGJE 


125 


violet,  dark  purple,  and  reddish-brown,  often  beautifully 
tinted.  In  general,  the  bodies  are  much  more  graceful 
and  delicate  than  those  of  the  brown  Algae.  There  is  the 


FIG.  117.— One  of  the  red  Algae. 

greatest  variety  of  forms,  branching  filaments,  ribbons,  and 
filmy  plates  prevailing;  and  often  profuse  branching  occurs, 
the  plants  resembling  mosses  of  delicate  texture  (Figs.  116 
and  117).  One  remarkable  group,  chiefly  displayed  on 
tropical  and  surf-beaten  coasts,  contains  such  a  deposit  of 
lime  in  the  cell-walls  that  the  forms  resemble  branching 
corals  or  coral-like  incrustations;  and  for  this  reason  they 
are  called  corallines. 

Red  Algae  are  all  anchored  forms,  and  are  chiefly  dis- 
played in  temperate  and  tropical  waters.     While  not  re- 


126 


A  TEXT-BOOK  OF  BOTANY 


stricted  to  any  special  depth,  they  are  characteristic  of  the 
deeper  waters  in  which  Algae  grow.  The  red  Algae  are  very 
little  used  by  man,  probably  the  most  conspicuous  article 
of  commerce  obtained  from  them  being  Irish  moss,  used  in 
jelly-like  preparations,  which  is  the  dried  bodies  of  certain 
forms  abundant  in  the  North  Sea. 

75.  Reproduction. — The  reproduction  of  the  red  Algae 
is  very  peculiar,  being  entirely  unlike  that  of  the  other 

Algae.  No  swimming  spores 
are  produced,  but  sporan- 
gia occur  that  produce  and 
discharge  spores  without 
cilia  and  hence  without  the 
ability  to  swim.  Since  each 
sporangium  usually  pro- 
duces four  such  spores, 
they  are  called  tetraspores 
(Fig.  118).  Floating  about 
in  the  water  instead  of 
actively  swimming,  they 

FIG.  118.— The  sporangium  (.4)  and  dis-    finally    germinate     and     pro- 
charged  tetraspores  (B)  of  one  of  the      ,  ,  1,1 

redAig£e.-AfterTHURET.  duce  new  plants,  as  do  the 

swimming  spores, 

The  sexual  reproduction,  however,  is  most  remarkable, 
but  is  too  complex  to  be  presented  in  any  detail  in  an 
elementary  text.  The  sperms,  like  the  tetraspores,  are 
without  cilia  and  simply  float  into  contact  with  the  oogo- 
nium,  whose  form  is  like  that  of  a  flask  with  a  long  narrow 
neck  (Fig.  119,  A).  In  the  bulbous  base  of  the  oogonium 
the  egg  is  developed.  In  a  very  simple  ease  the  floating 
sperm  comes  in  contact  with  the  long  neck,  the  two  walls 
become  perforated  at  the  point  of  contact,  the  contents  of 
the  sperm  enters  and  passes  to  the  egg,  and  thus  fertili- 
zation is  accomplished.  As  a  result  of  fertilization  there 
appears  on  the  plant  a  spore-containing  structure  like  a 


B 


ALG^E 


127 


little  fruit  (Fig.  119,  B  and  C,  and  Fig.  120).     The  spores 
it  contains  produce  the  alga  plants  again. 

Such  a  life-history  is  more  complex  than  any  thus  far 
given.  During  the  growing  season  the  tetraspores  multiply 
the  plant;  and  the  life-history  may  be  indicated  as  follows, 
P  designating  the  ordinary  plant  body : 

P — tetraspore — P — tetraspore — P — tetraspore,  etc. 

Such  a  series,  however,  does  not  continue  indefinitely; 
for  it  is  stopped  by  the  coming  of  an  unfavorable  period, 
such  a  period  as  winter  represents  to  many  plants.  In  the 
life-history  of  our  red  alga 
this  unfavorable  period  is 
bridged  by  the  fruit-like 
body,  just  as  in  the  other 
Algae  it  is  bridged  by  the 
heavy- walled  oospore.  Such 


FIG.  119.— One  of  the  red  Algae:  A, 
sexual  branches,  showing  antheridia 
(a),  odgonium  (o)  with  its  long  neck 
(0  to  which  are  attached  two  sperms 
(«);  B  and  C,  development  of  the 
fruit-like  body.— After  KNY. 


Fio.  120. — A  branch  of  one  of  the  red 
Algae  showing  a  mature  fruit-ljke 
body  (e),  with  escaping  spores  (a). 


128  A  TEXT-BOOK  OF  BOTANY 

a  life-history  may  be  indicated  as  follows,  a  formula  in 
which  the  fruit-like  body  is  designated  by  F: 

P\  -Spera>-spore-P  j  -Sperm>-spore-P,etc. 
I  —egg      /  I  -egg      / 

The  formula  shows  an  alternation  of  the  ordinary  plant 
body  and  the  fruit-like  body;  the  latter  always  resulting 
from  the  act  of  fertilization,  and  the  former  coming  from 
an  asexual  spore.  This  alternation  becomes  a  conspicuous 
feature  of  higher  plants. 


CHAPTER  VII 

FUNOI  ^ 

76.  General  characters. — The  Fungi  do  not  contain 
chlorophyll,  and  this  fact  forms  the  sharpest  contrast  be- 
tween them  and  the  Algae.  The  presence  of  chlorophyll 
enables  the  Alga3  to  be  independent  of  any  other  organism, 
since  they  can  manufacture  their  food  out  of  carbon  dioxide 
and  water  (§  14).  The  absence  of  chlorophyll  compels 
the  Fungi  to  be  dependent  upon  other  organisms  for  their 
food.  This  food  is  obtained  in  two  general  ways:  either 
(1)  directly  from  living  plants  and  animals,  or  (2)  from 
organic  waste  products  or  dead  bodies.  In  case  a  living 
body  is  attacked,  the  attacking  fungus  is  called  a  parasite; 
and  the  plant  or  animal  attacked,  the  host.  In  case  the  food 
is  obtained  in  the  other  way,  the  fungus  is  called  a  sapro- 
phyte. For  example,  the  rust  that  attacks  wheat  is  a 
parasite,  and  the  wheat  is  the  host;  while  the  mold  which 
often  develops  on  stale  bread  is  a  saprophyte. 

In  case  parasites  attack  valuable  plants  or  animals  they 
may  be  very  harmful,  giving  rise  to  destructive  diseases. 
The  United  States  Government  has  expended  a  great  deal 
of  money  in  studying  such  Fungi,  trying  to  discover  some 
method  of  destroying  them  or  of  preventing  their  attacks. 
There  is  an  interesting  selective  power  exhibited  by  many 
parasites,  that  restrict  themselves  to  certain  plants  and 
animals,  or  even  to  certain  organs.  Many,  however,  are 
more  general  in  their  attacks;  and  some  can  live  as  para- 
sites or  saprophytes  as  occasion  demands.  It  must  not  be 

129 


130  A  TEXT-BOOK  OF  BOTANY 

supposed  that  all  parasites  are  harmful  to  man  or  even 
destructive  to  their  host.  • 

In  the  case  of  saprophytes,  dead  bodies  or  body  products 
are  attacked,  and  sooner  or  later  all  organic  matter  is 
attacked  and  decomposed  by  them.  Were  it  not  for  them 
"the  whole  surface  of  the  earth  would  be  covered  with  a 
thick  deposit  of  the  animal  and  plant  remains  of  the  past 
thousands  of  years.'' 

The  parasitic  andsaprophytic  habits  are  not  restricted  to 
the  Fungi,  for  they  have  been  developed  also  by  some  of 
the  higher  plants;  but  by  far  the  largest  display  of  these 
habits  is  that  given  by  the  Fungi.  It  is  thought  that 
Fungi  have  been  derived  from  Algae;  that  is,  that  Fungi  are 
simply  Algse  that  have  learned  the  parasitic  or  saprophytic 
habit.  Some  of  them  resemble  certain  Algse  so  closely  that 
the  connection  seems  very  plain;  but  others  have  become 
so  modified  that  they  have  lost  all  likeness  to  the  Algse. 

No  attempt  will  be  made  to  present  even  an  outline  of 
the  classification  of  this  vast  and  perplexing  group.  A  few 
illustrations  will  be  seized  from  the  best-known  forms, 
especially  those  of  importance  to  man. 

77.  Bacteria. — Bacteria  include  the  smallest  known 
living  forms,  some  of  which  are  spherical  cells  only  5  0  >10  0  0 
inch  in  diameter.  It  is  estimated  that  1,500  of  certain 
rod-shaped  forms,  placed  end  to  end,  would  about  stretch 
across  the  head  of  an  ordinary  pin.  Even  to  distinguish 
ordinary  bacteria,  therefore,  the  highest  powers  of  the 
microscope  are  necessary;  and  to  study  them  is  too  difficult 
for  the  untrained  student.  However,  they  are  so  very  im- 
portant to  man,  on  account  of  their  useful  and  destructive 
operations,  that  every  student  should  have  some  informa- 
tion about  them.  Public  attention  has  been  drawn  to  them 
chiefly  on  account  of  the  part  they  play  in  many  infectious 
diseases,  in  which  connection  they  are  often  referred  to  as 
"microbes"  or  "germs." 


FUNGI  131 

Bacteria  are  found  almost  everywhere — in  the  air,  in 
the  water,  in  the  soil,  in  most  foods,  and  in  the  bodies  of 
plants  and  animals,  as  regular  inhabitants.  Many  of  them 
are  entirely  harmless,  some  are  useful,  and  others  are  very 
dangerous.  A  laboratory  near  Paris,  arranged  for  studying 
bacteria  in  the  air,  has  found  that  the  average  number  of 
bacteria  in  every  quart  of  air  in  that  locality  is  eighty. 
The  highest  numbers  were  found  during  the  autumn,  and 
the  lowest  during  the  winter;  while  a  wind  from  the  city 
increased  the  numbers  very  much.  The  "pure"  water  of 
springs  and  wells  contains  abundant  bacteria,  while  in 
stagnant  water  and  sewer  water  they  swarm  in  immense 
numbers.  The  slimy  deposits  usually  observed  about 
"iron"  and  "sulphur"  springs,  or  in  the  pipes  leading  from 
them,  are  due  to  the  presence  of  the  peculiar  bacteria  liv- 
ing in  such  waters.  The  presence  of  dangerous  bacteria 
in  drinking  water  is  probably  the  most  common  cause  of 
epidemics  of  infectious  diseases,  and  warnings  as  to  the 
•dangerous  condition  of  a  city  water-supply  should  always 
be  heeded.  It  is  very  evident  that  no  sewage  should  find 
its  way  into  such  water-supply. 

It  is  important  to  know  something  about  the  structure 
and  the  habits  of  bacteria,  before  considering  some  of  their 
important  relations  to  man.  They  are  one-celled  and  occur 
in  three  general  forms:  (1)  spherical  cells,  usually  grouped 
in  various  ways,  and  including  the  minutest  forms 
(Fig.  121,  B}}  (2)  rod-shaped  cells,  that  is,  longer  than 
broad,  the  cells  remaining  separate  or  attached  end  to  end 
and  forming  filaments  (Fig.  121,  F  and  <7);(3)  elongated 
•cells,  more  or  less  curved,  from  short  curved  forms  resem- 
bling a  comma  to  long  spirals  (Fig.  121,  J-Af).  Many 
bacteria  swim  more  or  less  actively  by  means  of  cilia;  and 
this  fact  first  gave  the  impression  that  they  are  minute 
animals — an  impression  that  is  still  prevalent  outside  of 
laboratories  (Fig.  121). 


A  TEXT-BOOK  OF  BOTANY 


Reproduction  is  by  cell-division,  as   among  the   blue- 
green  Algae  (§  58-60),  a  group  which  the  bacteria  resemble 


FIG.  121. — A  group  of  bacteria  of  various   kinds,  mostly  ciliated;  F  is   the  bac- 
terium of  typhoid  fever,  and  H  that  of  cholera. — After  EXGLER  and  PRAXTL. 

in  many  ways.     This  cell-division  is  remarkably  rapid  in 
bacteria,  resulting  in  such  a  prodigious  multiplication  of  in- 


FUNGI  133 

dividuals  in  a  comparatively  short  time  that  it  is  impossible 
to  imagine  what  would  happen  if  bacteria  were  left  free 
to  reproduce  to  their  full  capacity.  Bacteria  have  been 
observed  to  reproduce  themselves  in  fifteen  to  forty  minutes 
after  their  formation;  that  is,  a  single  generation  of  such 
bacteria  is  that  length  of  time.  It  would  be  interesting 
to  determine  the  number  of  progeny  from  a  single  bacterium 
at  the  end  of  twenty-four  hours,  if  such  a  rate  were  main- 
tained. When  nutrition  fails,  many  bacteria  have  the 
power  of  passing  into  a  protected  condition,  a  portion  of  the 
protoplasm  within  the  cell  separating  from  the  rest  and 
becoming  surrounded  by  a  thick  membrane  (Fig.  122). 
The  rest  of  the  cell  finally  disorganizes  and  this  internally 
formed  cell  persists.  It  has  received  the  name  of  "spore/* 
but  is  not  to  be  regarded  as  a  spore  in  the  usual  sense.  A 
single  bacterium  produces  only  one  such  spore,  and  when 
this  spore  again  encounters  favorable  conditions  it  produces 
in  turn  only  a  single  bacterium.  This  "spore,"  therefore, 
is  only  an  inactive  and  protected  condition  of  the  bacterium. 
It  is  of  great  importance  to  determine  the  power  of 
resistance  of  bacteria  and  of  their  more  resistant  "spores," 
and  there  is  great  variation  in  this  regard.  Drying  and 
cold  kill  many,  but  not  all.  For  example,  it  is  known  that 
the  bacterium  of  typhoid  fever  (Fig.  121,  F)  can  endure 
freezing  in  a  block  of  ice  for  months  and  become  active  again 
when  the  ice  melts;  and  for  this  reason  the  source  of  ice 
used  in  drinking  water  should  be  considered  as  carefully  as 
the  source  of  the  water  itself.  Moist  heat,  however,  as 
boiling  or  steaming,  has  been  found  to  be  most  efficient  in 
killing  bacteria;  and  so  the  boiling  of  water  and  the  cooking 
of  food  are  usually  ample  safeguards  against  them.  The 
so-called  disinfectants  are  chemicals  that  destroy  bacteria. 
It  is  the  knowledge  of  such  facts  that  has  developed  what  is 
called  antiseptic  surgery,  which  is  the  use  of  various  means 
to  exclude  bacteria  and  so  prevent  inflammation  and  decay. 


134 


A  TEXT-BOOK  OF  BOTANY 


The  most  important  relations  of  bacteria  to  man  may  be 
grouped  under  the  following  three  heads:  (1)  those  that 
induce  fermentation;  (2)  those  that  induce  disease;  (3)  and 
those  that  fix  nitrogen. 

(1)  Bacteria  that  induce  fermentation. — In  general,  fer- 
mentation is  the  decomposition  of  carbohydrates  and 
proteids  by  the  action  of  living  forms  directly  or  by  the 
enzymes  (§  47)  which  they  produce,  and  conspicuous  among 
these  forms  are  bacteria.  When  proteids  (meat,  etc.)  con- 
taining nitrogen  and  sulphur  are  decomposed  in  this  way, 
offensive  gases  are  liberated,  such  decomposition  being 
often  called  putrefaction.  When  the  word  fermentation  is 
ordinarily  used  it  refers  to  the  decomposition  of  sugars  in 


A  B  C 

FIG.  122. — Certain  bacteria  of  fermentation  and  disease:  bacteria  of  souring  milk 
(A),  of  vinegar  (B),  of  diphtheria  (C),  of  tetanus  or  lockjaw  (Z>);  C  and  D  show 
the  formation  of  the  so-called  "  spore." — After  FISCHER. 

solution,  as  in  various  fruit  juices,  which  breaks  them  up 
into  alcohol  and  carbon  dioxide,  the  latter  rising  as  bubbles 
through  the  solution,  which  is  then  said  to  be  working. 
Such  fermentations  are  produced  chiefly  by  yeasts,  which 
are  considered  in  the  next  section;  but  bacteria  are  con- 
cerned in  the  souring  of  milk  and  of  fruit  juices  and  in 
the  manufacture  of  vinegar  (Fig.  122).  These  saprophytic 
bacteria  that  induce  fermentation  and  putrefaction  are  of 
much  service  as  scavengers,  being  the  chief  agents  in  the 
destruction  of  dead  bodies.  The  various  processes  for 


FUXGI  135 

preserving  food   are   attempts   to   exclude    bacteria   that 
would  induce  fermentation  or  decay. 

(2)  Bacteria    that    induce    disease. — Fortunately    most 
bacteria  are  harmless,  for  they  are  constantly  present  in  the 
nostrils  and  mouth  and  alimentary  tract.     Even  those  that 
are  dangerous  may   be  resisted   successfully  and  fail   to 
develop  any  symptoms  of  disease.     When  the  resistance 
has  been  ineffectual  and  the  disease  has  developed,  the 
bacteria  may  produce  local  effects,  as  in  diphtheria  (Fig. 
122,  C)  and  in  typhoid  fever  (Fig.  121,  F);  but  the  most 
general  effect  is  from  the  production  of  poisons  (toxins) 
which  are  distributed  by  the  blood,  leading  to  fever,  de- 
lirium, etc.     These  poisons  are  different  for  each  disease, 
so  that  a  successful  antidote  (antitoxin)  for  the  diphtheria 
poison  has  no  effect  on  the  poison  of  the  bacterium  of 
typhoid  fever.     It  is  hoped  that  antitoxins  will  be  discov- 
ered for  all  such  bacterial  diseases,  among  which  are  not 
only  diphtheria  and  typhoid  fever,  but  also  cholera  (Fig. 
121,  //),  tuberculosis,  and  pneumonia.     Such  eruptive  dis- 
eases as  measles  and  scarlet  fever  have  not  yet  been  proved 
to  be  due  to  bacteria.    Among  plants  also  certain  bacterial 
diseases  occasion  great  loss,  as  pear  blight  and  peach  yel- 
lows, and  as  yet  have  baffled  those  seeking  for  remedies. 

(3)  Bacteria  that  fix  nitrogen. — It  will  be  remembered 
that  green  plants  manufacture  carbohydrates  from  carbon 
dioxide  and  water  (§  14);  but  that  in  the  manufacture  of 
proteids   from   carbohydrates   nitrogen   is   necessary.     Al- 
though free  nitrogen  constitutes  nearly  eight-tenths  of  the 
air,  plants  cannot  use  it  in  that  form,  but  must  obtain  it 
through  their  roots  from  certain  compounds  existing  in  the 
soil.     As  crops  are  removed,  the  nitrogen  supply  in  the  soil 
is  diminished,  and  presently  the  soil  becomes  so  impover- 
ished  that  it  is  said   to   be  exhausted.     To  restore   the 
fertility  of  the  soil,  the  farmer  has  learned  to  use  nitrogen- 
containing  fertilizers.     Through  the  removal  of  crops  and 

10 


136  A  TEXT-BOOK  OF  BOTANY 

in  various  other  ways  the  loss  of  available  nitrogen  for 
plants  is  enormous;  and  to  meet  this  loss  is  one  of  the  most 
important  problems,  for  the  known  sources  of  suitable 
fertilizers  cannot  yield  them  for  very  many  years. 

Since  an  endless  supply  of  free  nitrogen  exists  in  the  air, 
it  is  natural  to  turn  to  this  source  of  nitrogen  supply  for 
plants.  This  means  that  the  free  nitrogen  of  the  air  must 
be  "fixed "  in  some  combination  that  can  be  used  by  plants. 
It  is  just  here  that  bacteria  of  the  soil  play  a  very  important 
part.  Not  only  do  those  bacteria  that  produce  fermenta- 
tion and  decay  lay  hold  of  plant  and  animal  bodies  and 
produce  the  necessary  nitrogen-containing  substances  in 
the  soil,  but  certain  other  bacteria  of  the  soil  have  the 
power  of  fixing  the  free  nitrogen  of  the  air  into  compounds, 
and  hence  they  are  called  "nitrogen-fixing  bacteria."  If 
worn-out  land  lies  fallow  for  a  few  years  there  will  be  a 
slow  accumulation  of  nitrogen  salts  through  the  activity  of 
these  bacteria.  They  have  been  cultivated  artificially,  and 
it  is  hoped  that  such  cultures  will  be  obtained  that  it  may 
be  possible  to  use  them  to  inoculate  impoverished  land 
with  nitrogen-fixing  bacteria  and  so  hasten  its  restoration. 

A  peculiar  group  of  soil  bacteria  penetrates  the  roots  of 
certain  leguminous  plants,  as  clover,  alfalfa,  peas,  beans, 
etc.,  and  produces  little  wart-like  outgrowths  known  as 
root-tubercles  (Fig.  123).  The  cells  of  the  tubercles  swarm 
with  bacteria,  which  are  found  to  have  the  power  of  fixing 
the  free  nitrogen  of  the  air  circulating  in  the  soil.  As  a  con- 
sequence, such  plants  can  live  and  thrive  in  a  soil  exhausted 
of  its  nitrogen  salts,  and  can  be  used  in  restoring  the  soil. 
After  an  ordinary  crop,  such  as  wheat,  has  exhausted  the 
soil,  a  crop  of  clover  or  of  alfalfa  plowed  under  will  restore 
such  an  amount  of  nitrogen  salts  to  the  soil  that  it  can  be 
used  again  for  wheat,  often  with  a  surprising  yield.  This 
indicates  the  significance  of  what  is  called  rotation  of  crops. 

It  is  a  very  interesting  and  important  fact  that  these 


FUNGI 


137 


root-tubercle  bacteria  have  been  cultivated  artificially  at 
the  United  States  Department  of  Agriculture  in  such  a  way 


r 


FIG.   123.— Root-tuber 


feet  clover. 


that  they  can  be  shipped  anywhere  at  small  cost  and  used 
to  inoculate  soils  that  are  deficient  in  tubercle-forming  bac- 
teria. This  deficiency  may  be  discovered  either  by  the  ab- 


138 


A  TEXT-BOOK  OF  BOTANY 


sence  of  tubercles  on  the  roots  of  leguminous  plants  or  by 

the  failure  of  such  plants  to  grow  at  all. 

78.  Yeasts. — Yeasts  are  one-celled  plants  that  reproduce 

by  budding.  This  curious  method  consists  in  a  cell's  putting 
out  one  or  more  projections  which 
gradually  enlarge  and  finally  become 
pinched  off.  Often  the  cells  thus  pro- 
duced cling  together  in  short  irregu- 
lar chains  (Fig.  124).  The  chief  in- 
terest in  connection  with  yeasts  is 
the  important  part  they  play  in  the 
fermentation  of  sugar  solutions,  "  split- 
ting" the  sugar  into  alcohol  and  car- 
bon dioxide,  a  process  also  induced  by 
certain  bacteria  (§  77),  but  chiefly  by 
the  yeasts.  Fermentation  by  yeasts 

FIG.  124.— Yeast-ceils,  re-   is  employed  on  a   large  scale  in  the 
producing  by  budding,    manufacture  of  beer,  wine,  and  spirits. 

and  forming  chains.  *• 

and  in  the  making  of  bread.  In  the 
last-named  process,  the  dough  is  inoculated  with  yeast 
plants  and  placed  in  a  sufficiently  warm  temperature  to 
induce  rapid  growth.  The  plants  begin  to  reproduce  act- 
ively by  budding;  the  sugar  in  the  dough  is  split  into 
alcohol  and  carbon  dioxide ;  and  the  latter,  being  a  gas,  ex- 
pands and  puffs  up  the  dough,  making  it  light  and  porous, 
that  is,  causing  it  to  "rise." 

The  yeasts  commonly  used  have  been  cultivated  for 
centuries  and  are  not  known  in  the  wild  state.  There  are 
also  "wild  yeasts"  of  many  kinds,  and  many  spores  of  the 
higher  Fungi  behave  like  the  yeasts  in  budding  and  induc- 
ing fermentation.  The  "  working  "  of  yeast  may  be  demon- 
strated by  introducing  some  of  the  yeast  preparations  into  a 
solution  of  sugar  or  sirup  and  setting  it  in  a  warm  place. 
After  a  few  hours  the  bubbles  of  carbon  dioxide  should  be 
seen  rising  through  the  liquid. 


•  FUNGI 


139 


79.  Mucor. — One  of  the  most  common  of  the  Mucors,  or 
black  molds,  forms  white  furry  growths  on  damp  bread, 
preserved  fruits,  manure  heaps,  etc.  It  may  be  grown  easily 


FIG.  125. — Diagram  of  Mucor,  showing  the  profusely  branching  mycelium  and 
three  sporophores,  sporangia  forming  on  b  and  c. — After  ZOPF. 


FIG.  126.— Diagram  showing  mycelium  and  sporophores  of  Mucor. 


140 


A  TEXT-BOOK  OF  BOTANY 


B 


FIG.  127. — Developing  sporangia  of  Mucor: 
A,  swollen  tip  of  sporophore;  B,  wall 
separating  sporangium  from  the  rest  of 
the  body. 


by  keeping  a  piece  of  moist 
bread  in  a  warm  room  un- 
der a  glass  vessel.  The 
sources  of  its  food  supply 
indicate  that  it  is  a  sapro- 
phyte. 

The  body  of  Mucor  is 
a  good  illustration  of  the 
bodies  of  ordinary  Fungi. 
The  principal  part  of  the 
body  consists  of  colorless 
branching  threads,  either 
isolated  or  more  often  in- 
terwoven, and  is  called  the 
mycelium  (Fig.  125).  The 
interweaving  may  be  very 
loose,  the  mycelium  look- 
ing like  a  delicate  cobweb; 
or  it  may  be  close  and 


FIG.  128. — Mature  sporangium  of  Mucor, 
showing  wall  (a),  numerous  spores 
(c),  and  partition  wall  pushed  up  into 
the  cavity  of  the  sporangium  (6). 


FIG.  129. — Burst  sporangium  of  Mucor, 
the  ruptured  wall  not  being  shown, 
the  loose  spores  adhering  to  the  con- 
vex partition  wall  (see  Fig.  128). 


FUNGI 


compact,  forming  a  felt-like  mass,  as  may  be  seen  some- 
times in  connection  with  preserved  fruits.  The  mycelium 
is  in  contact  with  its  source  of  food-supply,  which  is 
called  the  substratum. 

From  the  prostrate  mycelium  numerous  erect  branches 
arise,  each  branch  bearing  at  its  tip  a  large  globular  cell 


FIG.  130. — Sexual  reproduction  ol  Mucar,  showing  tips  of  sexual  branches  in  con- 
tact (A),  the  two  gametangia  cut  off  by  partition  walls  (B),  and  the  heavy- 
walled  oospore  (C);  B  and  C  are  more  or  less  diagrammatic  as  to  cell  contents. 


containing  spores  (Figs.  126,  127,  128).  The  globular  cell, 
therefore,  is  a  sporangium,  and  the  erect  branch  is  a  sporo- 
phore  (spore-bearer).  The  sporangium  wall  bursts  (Fig. 
129),  the  light  spores  are  scattered  by  the  wind,  and  fall- 


1*2 


A  TEXT-BOOK  OF  BOTANY 


ing  upon  a  suitable  substratum  germinate  and  produce  new 
mycelia.  These  spores,  although  asexual,  are  evidently  not 
swimming  spores,  as  there  is  no  wrater  medium  for  them  to 
use.  This  method  of  transfer  being  impossible,  the  spores 
are  scattered  by  currents  of  air,  and  must  be  correspond- 
ingly light  and  powdery.  It  is  interesting  to  note  that  cer- 
tain molds  that  grow  in  the  water  develop  swimming  spores. 
While  the  ordinary  method  of  reproduction  through  the 
growing  season  is  by  means  of  these  rapidly  germinating 
spores,  in  certain  conditions  sexual  reproduction  also  occurs. 
Branches  put  forth  from  two  contiguous  mycelial  threads, 
the  tips  of  the  branches  being  in  contact  (Fig.  130,  A). 
Partition  walls  separate  the  tips  from  the  main  body  of  the 
plant  (Fig.  130,  B},  the  walls  in  contact  become  perforated, 
the  contents  of  the  two  tips  fuse,  and  a  heavy-walled 
oospore  is  the  result  (Fig.  130,  C).*  This  sexual  process 
suggests  that  of  Spirogyra  (§  69). 

80.  Peronospora. — These  are  the  downy  mildews,  very 
common    parasites    on    the    leaves    of    seed-plants.     The 

mycelium  is  entire- 
ly internal,  branch- 
ing among  the  tis- 
sues of  the  leaf,  and 
piercing  the  living 
cells  with  sucker-like 
branches  that  rap- 
idly absorb  their 
contents  (Fig.  131). 
The  presence  of  the 
parasite  is  made 

known  by  discolored  and  finally  deadened  spots  on  the 
leaves,  where  the  tissues  have  been  killed. 

*  It  is  not  easy  to  induce  Mucor  to  perform  the  sexual  process,  and 
in  fact  such  a  process  may  not  often  occur  in  nature. 


FIG.  131. — Branch  of  mycelium  of  Peronospora  in 
contact  with  two  cells  of  a  host  plant,  and  send- 
ing into  them  absorbing  branches. — After  DE 
BARY. 


FUNGI 


From  this  internal  mycelium  numerous  sporophores 
arise  and  reach  the  surface  of  the  leaf;  and  many  of  them 
rising  above  the  surface  close  together, 
they  form  little  velvety  patches  sug- 
gesting the  name  downy  mildew. 
These  sporophores,  after  rising  above 
the  surface  of  the  leaf,  branch  freely 
and  produce  spores  (Fig.  132).  The 
spores  are  scattered  by  the  wind,  fall 
upon  other  leaves,  and  start  new  my- 
celiu,  which  penetrate  into  the  tissues 
of  the  leaf  and  begin  their  ravages.  In 
this  way  the  parasite  spreads  with 
great  rapidity,  often  producing  seri- 
ous epidemics  among  plants. 

In  certain  conditions  special  branch- 
es arise  from  the  mycelium  which  bear 
antheridia  and  oogonia  that  remain 
within  the  host  (Fig.  133).  The  oogo- 
nium  develops  a  single  egg.  The  an- 
theridium  comes  into  contact  with  it, 
puts  out  a  tube  that  pierces  the  oogo- 
nium  wall,  and  discharges  its  contents 
(Fig.  133,  B).  As  a  result  of  this  act 


FIG.  132. — Sporophores  of 
a  Peronospara  form  ris- 
ing through  the  stomata 
of  the  host-leaf  (potato), 
branching,  and  bear- 
ing spores;  this  form 
causes  potato-rot. — Aft- 
er STRASBURGER. 


B 

FIG.  133.— Peronospora:  A,  oogonium  (o)  with  antheridium  (a)  in  contact;  B,  tube 
from  antheridium  penetrating  oogonium;  C,  oogonium  containing  oospore. — 
After  DEBARY. 


144  A  TEXT-BOOK  OP  BOTANY 

of  fertilization,  a  heavy- walled  oospore  is  formed  within  the 
oogonium  (Fig.  133,  C).  The  infected  leaves  containing 
the  oospores  fall  and  gradually  decay,  thus  liberating  the 
oospores,  which  are  free  to  germinate  during  the  next  spring 
and  infect  new  leaves. 

The  downy  mildews  include  some  very  destructive  par- 
asites, attacking  potatoes  (potato-rot),  grape-vines,  lima 
beans,  lettuce,  onions,  cucumbers,  melons,  radishes,  etc. 
Various  means  have  been  discovered  for  holding  these  dis- 
eases in  check. 

81.  Alga-like  Fungi. — Mucor  and  Peronospora  are  repre- 
sentatives of  a  large  group  (Phycomycetes)  of  Fungi  that 
most  resemble  Alga3,  and  suggest  clearly  that  they  are  Algae 
that  have  become  parasitic  or  saprophytic.     In  the  whole 
group  the  filaments  of  the  mycelium  are  coenocytic,  as  are 
the  bodies  of  the  group  of  green  Algse  to  which  Vaucheria 
belongs  (§  68).     They  reproduce  by  spores,  which  are  usu- 
ally scattered  by  the   wind,  and  also  produce  oospores. 
Some  of  them,  represented  by  Mucor,  have  similar  gametes, 
that  are  brought  together  in  a  way  that  suggests  the  Spiro- 
gyra  group  among  the  green  Algae  (§  69) ;  while  the  others, 
represented  by  Peronospora,  produce  eggs  and  sperms,  as 
in  the  case  of  Vaucheria,  though,  since  there  is  no  water 
connection,   the  sperm  reaches  the  egg   through  a  tube. 
Mucor  also  illustrates  the  saprophytes,  and  Peronospora 
the  internal  and  destructive  parasites. 

82.  Mildews. — The    true    mildews    are    very    common 
parasites  on  leaves  and  other    parts   of   seed-plants,  the 
mycelium  spreading  over  the  surface  like  a  cobweb.     They 
are  often  called   powdery  mildews  in  contrast  with  the 
downy  mildews  (§  80),  since  in  most  cases  they  look  like 
patches  of  whitish  powder  on  the  leaves.     A  very  com- 
mon form  occurs  on  lilac   leaves  (Fig.  134),  which  nearly 
always  show  the  whitish  patches  from  early  summer  until 
fall.      Other  common  mildews  attack  such  valuable  plants 


FUNGI 


145 


as  apple,  pear,  cherry,  rose,  hop,  grape,  wheat,  gooseberry, 
cucumber,  pea,  verbena,  sunflower,  aster,  etc.  In  fact,  very 
few  seed-plants  seem  to  escape  their  attacks.  Being  exter- 
nal parasites,  mildews  are  not 
necessarily  destructive ;  but 
they  often  cause  the  death  of 
the  host. 

An  examination  of  the  my- 
celium shows  that  its  filaments 
have  partition  walls;  and  hence 
the  body  is  not  coenocytic,  as 
in  Mucor  and  Peronospora,  but 
made  up  of  a  row  of  cells  as  in 
the  Conferva  forms  among  the 
green  Algae.  Small  disk-like 
outgrowths  are  sent  into  the 
epidermal  cells  of  the  host, 
anchoring  the  mycelium  and 
absorbing  the  cell  contents. 

During  the  summer,  numer- 
ous sporophores  arise  from  the 
mycelium,  not  bearing  sporan- 
gia, as  in  Mucor  (§  79),  but 
forming  spores  in  a  peculiar 

way.  The  end  of  the  sporophore  rounds  off,  almost  separat- 
ing itself  from  the  part  below,  and  becomes  a  spore.  Below 
this  another  organizes  in  the  same  way,  then  another,  until 
a  chain  of  spores  is  developed  (Fig.  135,  A),  easily  broken 
apart  and  scattered  by  the  wind.  Falling  upon  other  suit- 
able leaves,  these  spores  germinate  and  produce  new  my- 
celia,  enabling  the  parasite  to  spread  with  great  rapidity. 

The  mycelium  produces  also  minute  antheridia  and 
oogonia,  which  come  in  contact  with  one  another  as  do 
those  of  Peronospora  (§  80),  but  it  is  not  worth  while  for  the 
untrained  student  to  try  to  observe  them.  As  a  result  of 


FIG.  134.— Lilac  leaf  covered  -with 
mildew,  the  shaded  regions  repre- 
senting the  mycelium,  and  the 
black  dots  the  spore-cases. 


146 


A  TEXT-BOOK  OF  BOTANY 


fertilization,  however,  a  structure  called  the  spore-fruit  is 
developed.  These  spore-fruits  appear  on  infected  leaves  as 
minute  dark  dots  (Fig.  134),  each  one  being  a  sphere  of 

heavy-  walled  cells  (Fig.  135, 
B),  which  usually  bear  hair- 
like  appendages  of  various 
forms.  In  fact,  the  spore- 
fruit  is  a  heavy  protecting 
case  for  spores,  and  carries 
mildews  through  the  winter 
or  the  dry  season.  The  ap- 
pearance of  a  many-celled 
spore-case  as  the  result  of 
fertilization,  rather  than  a 
new  mycelium,  suggests  the 
similar  result  of  fertilization 
among  the  red  Algse  (§  75). 
By  bursting  the  wall  of 

this    Spore-fruit,    One    Or    more 

jv  uiJJ        vi 

delicate    bladder-like    SaCS    are 


FIG.  135.—  Reproduction  of  mildew: 
A,  chain  of  spores  developed  by  a 
sporophore;    B,  spore-case  burst, 
and    showing    the    extruded    sac      extruded,      and      through      the 
(ascus)    with    its    spores.  —  After 

TULASNE.  transparent  wall  of  each  sac 

several  spoies    may    be    seen 

(Fig.  135,  B).  The  delicate  sacs  are  called  asci  (singular, 
ascus),  &  word  meaning  "sacs,"  and  hence  the  great  group 
of  Fungi  represented  here  by  the  mildews  is  named  the 
Ascomycetes,  which  means  "sac  Fungi."  In  the  life-history 
of  the  mildews  it  is  evident  that  there  are  two  kinds  of 
asexual  spores:  those  produced  in  chains  by  the  sporophores, 
and  those  produced  in  the  sacs  of  the  spore-fruit.  Both 
produce  new  mycelia,  the  latter  starting  the  first  mycelia 
of  the  growing  season,  and  the  former  multiplying  mycelia 
throughout  the  growing  season. 

83.  Other  Sac  Fungi.  —  The  group  of  sac  Fungi  is  a  very 
large  one,  containing  many  forms  that  are  well  known  and 


FUNGI 


some  that  are  important.  All  of  them,  at  some  period  of 
the  life-history,  produce  spores  in  sacs,  and  the  sacs  are 
usually  contained  in  a  spore- 
fruit.  The  spore-fruit  is  of  three 
general  kinds:  (1)  a  hollow  sphere, 
completely  enclosing  the  sacs;  (2) 
a  flask-like  structure  with  a  small 
open  neck;  and  (3)  a  cup-like  or 
saucer-like  structure  which  is 
lined  by  a  layer  of  sacs. 

The  first  kind  of  spore-fruit  is 
illustrated  by  the  mildews  just 
described.  It  is  of  interest  to 
know  that  truffles  are  such 
closed  spore-fruits,  having  be- 
come large  and  edible.  The 
truffle  Fungi  are  saprophytic, 
the  mycelium  being  found  espe- 
cially in  forests  under  decaying 
leaves.  The  truffles  of  commerce 
are  obtained  chiefly  from  France 
and  Italy. 

The  sac  Fungi  with  flask-like 
spore-fruits  are  illustrated  by 
many  forms  growing  on  dead 
wood  or  as  parasites  under  the 
bark  of  trees  and  shrubs,  and 
forming  upon  the  surface  of  the 
bark  black,  wart-like  growths 
that  include  the  spore-fruits,  in 
plum-  and  cherry-trees  produc- 
ing the  disease  known  as  black 
knot.  An  important  member  of 

this  group  is  the  fungus  that  produces  the  ergot  of  medi- 
cine.     It  is  parasitic  upon  the  young  heads  of  rye  and 


FIG.  136.— Head  of  rye  attacked 
by  ergot  fungus,  conspicuous 
growths  replacing  the  grains  of 
rye. — After  TULASNE. 


14S 


A  TEXT-BOOK  OP  BOTANY 


other  grasses,  distorting  them  and  producing  the  excrescent 
growths  from  which  the  ergot 
is  obtained  (Fig.  136). 


FIG.  137.— Two  kinds  of  cup-fungus. 
— After  LINDAU. 


Flo.  138. — A  cup-fungus  growing  on  a 
spruce. — After  RKHM. 


Most  attractive,  however,   is  the  group  of  sac  Fungi 

with  spore-fruits  shaped 
like  saucers,  cups,  funnels, 
flat  disks,  etc.;  for  the 
lining,  made  up  of  a  layer 
of  the  spore  -  containing 
sacs,  is  often  some  brilliant 
shade  of  red,  yellow,  or 
brown  (Figs.  137  and  138). 
The  scarlet-lined  cups  of 
certain  forms  are  often 
seen  on  decaying  logs, 
stumps,  etc.;  and  in  the 
morels  the  spore-fruits  get 
so  large  and  fleshy  that 
they  are  used  as  one  of  the 
most  delicate  of  the  edible 
mushrooms,  although  they 


FIG.  139.— The  common  edible  morel,  the 
depressions  in  the  surface  being  lined 
by  a  layer  of  asci.— After  GIBSON. 


are  not  mushrooms  at  all 
(Fig.  139). 


FUNGI 


1  »'.» 


84.  Rusts. — Rusts  are  destructive  parasites  that  attack 
almost  all  seed-plants,  but  those  that  attack  the  cereals 
arc  of  -perial  importance.  Wheat,  oats,  rye,  and  barley 
all  have  their  rusts;  and  in  the  United  States  there  is 
a  yearly  loss  of  several  million  dollars  on  account  of  the 
ravnu'  •<  «>f  the  wheat -rust  alone,  scarcely  a  field  being  en- 
tirely free  from  the  pest.  Naturally  these  parasites  have 
been  investigated  persistently;  but  while  very  much  has 
been  learned  about  their  life-histories  and  behavior,  no 
remedy  has  been  discovered.  It  has  been  found  that  certain 
varieties  of  wheat  resist  the  rust  better  than  others,  and 
that  varieties  ripening  early  escape  serious  injury;  and 
these  facts  may  lead  to  the  breeding  of  resistant  and  early 
races. 

The  life-history  of  a  rust  is  usually  very  complex,  since 
there  are  several  phases  in  the  history,  and  all  the  phases 
may  not  occur  on  the  same  host  plant.  Since  wheat-rusts 
are  better  known  than  any  other, 
one  of  them  may  be  used  to  illus- 
trate  the  life-history. 

While  the  leaves  and  the  stems 
of  wheat  are  growing,  tn(l  mycelium 
of  the  parasite  is  burrowing  among 
the  tissues  of  infected  plants.  About 
the  time  of  harvest,  numerous  sporo- 
phores  arise  from  the  mycelium  and 
reach  the  surface  of  leaves  and 
st.-tns,  each  sporophore  producing 
at  its  tip  a  reddish  spore  (Fig.  140). 

These  are  the  summer  spores,  and  they  occur  in  such  great 
numbers  that  they  form  rusty-looking  lines  and  spots, 
giving  name  to  the  disease.  The  summer  spores  are  scat- 
tered freely  by  the  wind;  and  those  falling  upon  other 
plants  germinate  immediately,  the  new  mycelium  pene- 
trating the  host  plant,  and  lie^inning  its  ravages.  By 


Fio.  140.— The  summer  spores 
of  wheat-rust. 


150 


A  TEXT-BOOK  OF  BOTANY 


FIG.  141.— The  winter 
spores  of  wheat-rust. 


means  of  these  summer  spores  the  rust  may  spread  through 
a  field  of  wheat  and  into  adjoining  fields  with  great 
rapidity. 

Later  in  the  season,  on  the  stubble 
and  on  plants  not  removed  in  the  har- 
vesting, black  lines  and  dots  appear, 
which  are  masses  of  a  very  different  kind 
of  spore  sent  to  the 
surface  by  the  myce- 
lium (Fig.  141).  This 
spore,  which  is  two- 
celled  and  has  a  very 
heavy  wall,  is  the 
winter  spore;  for  it  is 
in  this  form  that  the 
rust  usually  endures  the  winter. 

In  the  spring  the  winter  spores,  lying 
where  the  plants  on  which  they  were 
produced  have  decayed,  begin  to  ger- 
minate, each  one  of  the  two  cells  send- 
ing out  a  short  filament.  This  filament 
is  not  a  parasite,  but  a  saprophyte,  and 
usually  consists  of  four  cells,  each  one 
of  which  sends  out  a  little  branch,  at 
the  tip  of  which  a  small  spore  is  pro- 
duced (Fig.  142).  These  may  be  called 
early  spring  spores. 

These  early  spring  spores  are  scat- 
tered by  the  wind;  and  those  falling 
upon  barberry  leaves  germinate,  the 
new  mycelia  entering  and  spreading 
through  the  leaves.  In  this  phase  the 
rust  is  parasitic  upon  an  entirely  dif- 
ferent host,  and  one  that  holds  no  relation  to  wheat.  The 
mycelium  in  the  barberry  leaves  sends  to  the  leaf  surface, 


FIG.  142.— A  winter 
spore  of  wheat  -  rust 
germinating,  each  fila- 
ment producing  four 
cells,  each  of  which 
sends  out  'a  branch 
that  produces  at  its  tip 
a  spore  (early  spring 
spore).  —  After  Tu- 
LASNE. 


FUNGI 


151 


Fio.  143. — A  cluster-cup  (on  barberry)  of  wheat-rust 
containing  chains  of  spring  spores. — After  STRAS- 

BURGER. 


usually  the  under  one,  groups  of  sporophores,  each  group 
surrounded  by  a  cup-like  structure;  and  hence  these  cup- 
like  clusters  have  been  called  cluster-cups.  In  these  cluster- 
cups  the  spores  oc- 
cur in  long  chains, 
and  may  be  called 
spring  spores  or  clus- 
ter-cup spores  (Fig. 
143). 

These  spring 
spores  on  the  bar- 
berry leaves  are 
scattered  by  the 
wind  and  infect 
young  wheat  plants; 
that  is,  germinate 
and  produce  myce- 
lia  which  penetrate 

them.  These  new  mycelia  later  put  forth  the  summer 
spores,  and  in  this  way  the  life  cycle  has  returned  to  the 
point  with  which  this  account  began. 

It  will  be  noted  that  in  this  life-history  there  are  four 
kinds  of  spores:  (1)  the  early  spring  spores,  produced  by  a 
simple  saprophytic  filament,  and  infecting  barberry  leaves; 
(2)  the  spring  or  cluster-cup  spores,  produced  by  a  mycelium 
parasitic  on  the  barberry,  and  infecting  young  wheat 
plants;  (3)  the  summer  spores,  produced  by  a  mycelium 
parasitic  on  wheat,  and  infecting  other  wheat  plants;  (4) 
the  winter  spores,  produced  by  the  same  mycelium,  and  in 
spring  producing  the  saprophytic  filaments.  In  the  United 
States  the  barberry  is  not  widely  distributed  enough  to  play 
so  important  a  part  in  the  life-history  of  wheat-rust,  and 
other  seed-plants  have  been  found  to  be  used  as  hosts  for 
the  cluster-cup  stage  of  certain  forms  of  rust.  It  is  also 
stated  that  the  cluster-cup  stage  may  be  omitted,  in  that 
11 


152 


A  TEXT-BOOK  OF  BOTANY 


case  the  early  spring  spores  infecting  wheat  plants  rather 
than  barberry  leaves;  and  recently  it  has  been  shown 
that  often  the  summer  spores  survive  the  severest  winter 
and  infect  young  wheat  plants  of  the  next  season. 

Another  well-known  rust  is  that  which  attacks  apple- 
trees  and  their  relatives,  the  wild  crab,   hawthorn,  etc. 
The  stage  on  the  apple-tree  is  the  clus- 
ter-cup stage,  the  cluster-cups  occurring 
on  the  under  surface  of  the  leaves;  the 
mycelium  also   attacks   and   ruins    the 
fruit,    the    cluster-cups    being   seen    in 
connection    with    the    diseased    parts. 
The  cluster-cup  spores  infect  the  cedars, 
producing    swellings     half 
an  inch  or  more  in  diame- 
ter and  known   as   cedar- 
apples  (Fig.  144).     In  the 
spring   these    cedar-apples 
become  conspicuous,  espe- 
cially after  a    rain,   when 
the   jelly-like   masses  con- 
taining the  orange-colored 
spores  swell.     These  spores 
are  blown    about   and  in- 
fect the  apples.     Attempts 
are  made  to  check  the  ap- 
ple-rust by  destroying  the 
cedar-trees  and  by  spray- 
ing the   apple-trees,  when 

they  are  putting  out  their  leaves,  with  a  liquid  that  kills 
such  Fungi. 

Although  rusts  possess  several  kinds  of  ordinary  (asex- 
ual) spores,  no  oospores  (sexually  formed  spores)  have  been 
observed;  but  a  process  in  the  life-history  representing  a 
sexual  act  has  been  discovered  in  some  forms. 


FIG.  144.— A  cedar-apple. 


FUN(JI 


153 


85.  Mushrooms. —  This 
name  is  a  very  indefinite 
one;  sometimes  applying 
to  any  of  the  fleshy  Fungi 
of  the  umbrella  form,  and 
sometimes  including  among 
such  forms  only  those  that 
are  edible,  the  poisonous 
ones  being  spoken  of  as 
toadstools.  For  our  pur- 
pose, no  exact  definition 
of  the  word  is  necessary, 
it  being  used  as  the  com- 
mon name  of  a  group  of 
forms  with  which  the  stu- 
dent should  be  somewhat 
familiar. 

The  life-history  of  the 


Fio.  145.— Mycelium  of  a  mushroom  produo- 


Ordinary   edible    mushroom       ing  sporophores  (buttons) .—After  SACHS. 


FIG.  146. — A  common  edible  mushroom  (Lepiota). 


154: 


A  TEXT-BOOK  OF  BOTANY 


of  the  markets  will  serve  as  an  illustration.  The  myce- 
lium of  white  branching  threads  spreads  extensively  through 
the  substratum  of  decaying  organic  material,  and  by  those 

who  grow  mush- 
rooms is  called 
spawn.  This  my- 
celium, although 
the  least  conspicu- 
ous part  of  the 
mushroom,  is,  of 
course,  the  real 
vegetative  body. 
Upon  this  under- 
ground mycelium 
little  knob-like  pro- 
tuberances arise 
(buttons),  growing 
larger  and  larger 
(Fig.  145)  until 
they  develop  into 
the  umbrella  -  like 
structures  common- 
ly spoken  of  as 
mushrooms  (Fig. 
146).  This  um- 
brella-like struc- 
ture, however,  cor- 
responds to  the 
sporophores  that 
arise  from  the  my- 
celia  of  other  groups 
of  Fungi,  except 
that  it  includes  a  large  number  of  sporophores  organized 
into  a  single  large  body.  Therefore,  the  real  mushroom 
body  is  a  subterranean  mycelium,  upon  which  the  struc- 


Fio.  147. — Sections  through  the  gills  of  a  common 
mushroom:  A,  gills  hanging  from  the  pileus;  B, 
single  gill  showing  the  basidium  layer;  C.  much 
enlarged  view,  showing  the  basidia-bearing  spores. 
— After  SACHS. 


FUNGI 


155 


tures  commonly  called  mushrooms  are  the  spore-bearing 
branches.  In  pulling  up  a  mushroom,  fragments  of  the 
mycelium  may  often  be  seen  attached  to  it,  looking  like 
small  rootlets.  In  the  following  description,  however,  the 
word  mushroom  will  be  used  in  its  ordinary  sense. 

The  mushroom  has  a  stalk-like  portion  (stipe}  and  an 
expanded  umbrella-like  top  (pileus).  On  the  under  side  of 
the  pileus  there  are  found  thin,  radiating,  knife-blade-like 
plates  (gills}  (Fig.  147,  A).  The  surface  of  the  gills  consists 
of  a  layer  of  peculiar  club-shaped  cells  called  basidia  (Fig. 
147,  B).  From  the  broad  end  of  each  basidium  usually 
four  delicate  branches 
arise,  each  producing  at 
its  tip  a  minute  spore 
(Fig.  147,  C).  The  ripe 
spores  shower  down  from 
the  gill  surfaces,  germinate, 
and  produce  new  mycelia. 

The  most  common  edi- 
ble mushrooms  grow  in 
fields  and  pastures;  but 
there  are  numerous  mush- 
rooms in  the  deep  woods, 
in  fact  wherever  there  is 
decaying  organic  material. 
It  has  been  found  impos- 
sible to  give  directions  for 
distinguishing  edible  and 
poisonous  forms  that  can 
be  used  by  those  who  are 

not  familiar  with  mushrooms.  It  is  exceedingly  unsafe  for 
an  inexperienced  person  to  gather  wild  mushrooms  for  eat- 
ing, for  some  of  the  deadliest  forms  resemble  in  a  general 
way  those  commonly  eaten. 

The  mushrooms  with  gills  form   a   very   large    group, 


FIG.  148.— A  common  pore-fungus. — 
After  GIBSON. 


156 


A  TEXT-BOOK  OF  BOTANY 


but  numerous  forms  display  the  spore-producing  layer  in 
other  ways.  For  example,  the  pore  Fungi  are  so  named 
because  they  have  pore-like  depressions  or  tubes  lined  by 
the  basidium-layer,  instead  of  gills.  In  addition  to  umbrella- 
like  forms  among  the  pore  Fungi  (Fig.  148),  there  are  the 
numerous  bracket  Fungi,  which  appear  as  hard  hoof-like 
outgrowths  on  tree  trunks  (Fig.  149),  stumps,  etc.  Some 


149. — A  bracket-fungus  (pore-fungus)  growing  on  red  oak. 


of  these  bracket  Fungi  are  perennial,  showing  annual  lay- 
ers of  growth,  as  the  common  touchwood  or  punk.  Other 
*  mushrooms  have  the  umbrella-like  bodies,  but  instead  of 
either  gills  or  pores,  there  are  spine-like  processes  coated  by 
the  spore-forming  layer  (Fig.  150);  others  appear  as 


FUNGI 


157 


gelatinous,  dark-brown,  shell-shaped  masses,  resembling 
ears;  still  others  resemble  fleshy  branching  corals  (Fig.  151), 
and  hence  are  called  coral  Fungi. 

In  general,  mushrooms  are  harmless  and  often  useful 
saprophytes,  but  there  are  also  destructive  parasitic  forms 


FIG.  150.— Mushroom  with  spine-like 
processes  instead  of  gills.  —  After 
GIBSON. 


Fio.   151.— The  common  edible  coral 
fungus. — After  GIBSON. 


that  attack  forest-trees.  The  mycelium  usually  spreads 
between  the  bark  and  the  wood,  sending  special  absorbing 
branches  into  the  wood,  often  even  into  the  heart  wood, 
causing  decay  and  weakening  of  the  stem.  The  spore- 
bearing  structures  are  sent  to  the  surface,  and  appear  as 
toadstools,  bracket  Fungi,  etc.  Spores  are  produced  in 
great  profusion  and  infect  other  trees,  the  new  mycelium 
using  wounds  to  effect  its  entrance.  Some  mycelia  spread 
through  the  soil,  inoculating  trees  through  their  roots;  while 


158 


A  TEXT-BOOK  OF  BOTANY 


in  other  cases  the  spores  are  scattered  by  the  wind  and  the 
infection  starts  in  the  tree  tops.  Almost  all  full-grown  trees 
are  diseased  at  some  point. 

86.  Puffballs.—  The  puffballs  are  fleshy  Fungi  that  differ 
from  the  mushrooms  in  having  the  spores  enclosed  until 

they  are  ripe  (Fig.  152). 
There  is  a  subterranean 
mycelium,  as  in  the  mush- 
rooms; but  the  spore- 
bearing  structure  is  a 
fleshy,  globular  body,  con- 
taining irregular  cham- 
bers lined  with  the  spore- 
producing  layer.  When 
young,  this  body  is  solid 
and  white;  but  as  the 
spores  mature,  it  becomes 
yellowish  and  brownish, 
gradually  dries  up,  and 
finally  is  only  a  brown 
parchment-like  shell  con- 
taining innumerable,  ex- 
ceedingly small  spores 
that  are  discharged  by 

the  breaking  of  the  shell.  Some  of  the  puffballs  become 
very  large,  reaching  a  diameter  of  twelve  to  eighteen 
inches. 

87.  The  highest  group  of  Fungi. — The  rusts,  mushrooms, 
and   puffballs  represent   the   highest   and   most  extensive 
group  of  Fungi,  characterized  by  producing  spores  by  means 
of  a  basidium,  and  hence  called  Basidiomycetes,  which  means 
"basidium  Fungi."     The  peculiarity  of   the  basidium   is 
that  it  sends  out  branches,  each  of  which  produces  a  spore 
at  its  tip  (Fig.  147,  C).     The  layers  of  basidia  (spore-pro- 
ducing cells)  were  noted   in  the  mushrooms  and  the  puff- 


FIG.  152.— Puffballs.— After  GIBSON. 


FUNGI 


159 


balls:  but  it  is  thought  that  a  basidium  is  represented  also 
in  the  life-history  of  the  rusts,  and  hence  they  are  now 
included  among  the  Basidiomycetes.  This  supposed  ba- 
sidium of  the  rust  is  the  little  filament  produced  by  the 
winter  spore,  which  sends  out  branches  that  bear  the  small 
early  spring  spores  (§  84). 

88.  Mycorhiza. — This  name  means  root-fungus,  and 
refers  to  an  association  that  exists  between  certain  Fungi 
of  the  soil  and  the  roots  of  higher  plants.  It  was  thought 
once  that  this  association  of  fungus  and  root  occurred  only 
in  connection  with  a  limited  number  of  higher  plants, 
such  as  orchids,  oaks,  heath  plants,  etc.;  but  more  recent 
study  indicates  that  probably  the  large  majority  of  vascular 
plants,  that  is,  plants  with  true  roots,  have  developed  this 
relation  to  a  soil  fungus,  the  water-plants  being  excepted. 
It  has  been  found  that  the  humus  soil  of  forests  is  in  large 
part  "a  living  mass  of  innumerable  filamentous  Fungi." 

It  is  of  advantage  to  roots  to  relate 
themselves  to  this  great  network 
of  filaments,  which  are  already  in 
the  best  relations  for  absorption; 
and  those  plants  which  are  unable 
to  do  this  are  at  a  disadvantage  in 
the  competition  for  the  nutrient 
materials  of  the  forest  soil.  It  is 
doubtful  whether  many  vascular 
green  plants  can  absorb  from  the 
soil  enough  for  their  needs  with- 
out this  assistance;  and  if  this  is 
true,  the  mycorhiza  Fungi  become 


FIG.  153.— Mycorhiza :   the  tip 

of  a  beech  rootlet  enmeshed    of  vital  importance  in  the  nutri- 

by    a    soil    fungus.  —  After 
FRANK. 


tion  of  such  plants.     The  delicate 
branching  filaments  of  the  mycelium 

either  enwrap  the  rootlets  with  a  jacket  of  interwoven  threads 
(Fig.  153),  or  occur  within  the  cortical  cells  of  the  root. 


160 


A  TEXT-BOOK  OF  BOTANY 


89.  Lichens. — Lichens  are  abundant  everywhere,  form- 
ing splotches  of  various  colors  on  tree  trunks,  rocks,  old 


FIG.  154. — A  common  lichen  growing  on  bark;  the  numerous  dark  disks  are  lined 
by  a  layer  of  asci. 

boards,  etc.,  and  growing  also  upon  the  ground  (Figs.  154 
and  155).  They  have  a  general  greenish-gray  color,  but 
brighter  colors  also  may  be  observed. 

The  great  interest  connected  with  lichens  is  that  they 


FIG.  155. — A  common  foliose  lichen  growing  upon  a  board. 


FUNGI 


161 


are  not  single  plants,  but 
that  each  lichen  is  formed 
of  a  fungus  and  an  alga 
living  together  so  inti- 
mately as  to  appear  like 
a  single  plant.  In  other 
words,  a  lichen  is  not  an 
individual  but  a  firm  of 
two  individuals,  very  un- 
like one  another.  If  a 
lichen  be  sectioned,  the 
relation  between  the  two 
constituent  plants  may  be 
seen  (Fig.  156).  The  fun- 
gus makes  the  bulk  of  the 
body  with  its  interwoven 
mycelial  threads,  in  the 
meshes  of  which  lie  the 
Algae,  sometimes  scattered, 
sometimes  massed.  It  is 

these  enmeshed  Algae,  showing  through  the  transparent  my- 
celium, that  give  the  greenish  tint  to  the  lichen. 


Fio.  156. — Cross-section  of  a  lichen,  show- 
ing the  interwoven  mycelium  of  the 
fungus  (TO)  and  the  enmeshed  alga  (g). 
— After  SACHS. 


Fio.  157.— Section  of  one  of  the  cup-like  bodies  of  a  lichen,  showing  the  stalk  of  the 
cup  (m),  the  masses  of  Algae  (g),  and  the  lining  layer  of  asci  (A).— After  SACHS. 


162 


A  TEXT-BOOK  OF  BOTANY 


It  has  been  found  that  the  lichen-alga  can  live  quite 
independently  of  the  lichen-fungus.  In  fact,  the  enmeshed 
Algae  are  often  recognized  as  identical  with  forms  living 
independently,  the  forms  usually  being  certain  blue-green 


FIG.  158.— Much   enlarged   section   of  portion  of  lining  layer,   showing  the  asci 
(1,  2,  3,  4)  with  their  contained  spores. — After  SACHS. 

Algae  and  some  of  the  simpler  green  Algae.  On  the  other 
hand,  it  has  been  found  that  the  lichen-fungus  is  com- 
pletely dependent  upon  the  Algae;  for  the  germinating 
spores  of  the  fungus  do  not  develop  far  unless  the  young 


FUNGI 


163 


mycelium  can  lay  hold  of  suitable  Algae.  Artificial  lich- 
ens also  have  been  made  by  bringing  together  wild  Algae 
and  lichen-fungi.  Lichens,  therefore,  are  really  combina- 
tions of  a  parasitic  fungus  and  its  host,  the  parasitism 
being  peculiar  in  that  the  host  is  not  injured.  The  fungus 
lives  upon  the  food  made  by  the  alga,  and  the  relation 
suggested  is  that  the  alga  is  enslaved  by  the  fungus. 

At  certain  times  cup-like  or  disk-like  bodies  appear  upon 
the  surface  of  the  lichen,  with  brown  or  black  or  more 
brightly  colored  lining  (Fig.  154).  A  section  through  these 


FIG.   159.— Fruticose  lichens:    -4,  a  simple  form;  B.  reindeer  moss;   C,  &  common 
hanging  lichen. — A  and  B  after  STRASBURGER;  C,  after  SACHS. 


bodies  shows  that  the  colored  lining  is  largely  made  up 
of  delicate  sacs  containing  spores  (Figs.  157  and  158).  It 
is  evident,  therefore,  that  such  a  lichen-fungus  is  one  of  the 
Ascomycetes  (§  82),  and  it  is  this  group  of  Fungi  that 


164  A   TEXT-BOOK  OF  BOTANY 

is  chiefly  concerned  in  forming  lichens.  Some  Basidio- 
mycetes  also  have  learned  to  form  lichens. 

Various  forms  of  lichens  can  be  distinguished  as  fol- 
lows: (1)  crustaceous  lichens,  in  which  the  body  resembles 
an  incrustation  upon  its  substratum  of  rock,  soil,  etc.; 
(2)  foliose  lichens,  with  flattened,  leaf-like,  lobed  bodies, 
attached  only  at  the  middle  or  irregularly  to  the  substra- 
tum (Fig.  155);  (3)  fruticose  lichens,  with  slender  bodies 
branching  like  shrubs,  either  erect,  hanging,  or  prostrate 
(Fig.  159). 

Lichens  are  often  very  important  in  starting  a  humus 
formation  on  bare  rocks  and  sterile  soil.  In  such  exposed 
situations  Algae  could  not  endure  alone,  and  of  course 
Fungi  could  not  exist  alone  in  any  situation.  The  lichen 
combination  can  exist,  however,  since  the  fungus  obtains 
its  food  from  the  Algae,  while  the  latter  are  protected  against 
drying  out  by  the  enveloping  meshwork  of  the  fungus.  As 
the  lichens  grow  and  decay,  enough  humus  is  collected  for 
higher  forms  of  plant  life  to  start;  and  these  in  turn  con- 
tribute to  a  more  rapid  accumulation  of  humus,  until 
presently  a  respectable  soil  may  be  the  result. 


CHAPTER  VIII 

LIVERWORTS 

90.  Summary. — As  an  introduction  to  liverworts  it  is 
well  to  state  the  most  important  facts  in  reference  to  the 
Algse  and  Fungi.  The  Algae  and  Fungi  together  consti- 
tute the  first  great  division  of  the  plant  kingdom,  known 
as  Thallophytes.  The  name  means  "thallus  plants,"  and 
"thallus"  means  a  body  usually  prostrate  and  having  no 
special  vegetative  organs  as  leaves  and  roots.  Such  a 
definition  cannot  be  very  rigid,  for  some  Algae  cannot  be 
said  to  have  strictly  thallus  bodies,  and  in  the  higher  groups 
thallus  bodies  also  occur;  but  the  name  is  a  convenient  one 
to  apply  to  all  plants  below  the  liverworts. 

As  the  study  of  the  higher  plants  is  begun,  the  important 
progress  made  by  the  Thallophytes  must  be  kept  clearly  in 
mind,  for  the  liverworts  start  with  this  progress  behind 
them.  The  important  progress  may  be  stated  as  follows: 

(1)  Increasing  complexity  of  the  plant  body. — Beginning 
with   single   isolated   cells,   the   plant   body   reaches   con- 
siderable complexity  among  the  Thallophytes,  in  the  form 
of  simple  or  branching  filaments,  plates  of  cells,  and  masses 
of  cells. 

(2)  Appearance  of  spores. — Beginning  with  reproduction 
by  vegetative  multiplication,  the  Thallophytes  soon  develop 
special  cells  for  reproduction  (spores) ,  and  produce  them  not 
only  in  abundance  but  in  a  variety  of  methods  and  forms. 

(3)  Appearance  of  sexual  cells. — After  ordinary  spores 
appear,  the  Thalloph-ytes  also  introduce  a  third  form  of 

165 


166  A   TEXT-BOOK  OF  BOTANY 

reproduction  by  producing  sexual  cells  (gametes),  which  by 
fusing  in  pairs  (fertilization)  form  oospores.  At  first  the 
pairing  gametes  are  alike,  but  later  they  become  very 
different,  and  are  called  sperms  and  eggs.  The  organ  pro- 
ducing sperms  is  called  the  antheridium,  and  that  pro- 
ducing an  egg  the  oogonium;  and  among  the  Thallophytes 
each  of  these  organs  consists  of  a  single  cell. 

(4)  Algce  the  independent  line. — This  means  not  only  that 
the  Fungi  have  probably  been  derived  from  the  Alga?  by 
losing  the  ability  to  make  their  own  food,  but  also  that  the 
higher  plants  have  been  derived  from  the  Algae.  Accord- 
ingly the  liverworts,  about  to  be  studied,  are  believed  to 
have  developed  from  the  Algae. 

91.  General  character  of  Liverworts. — Liverworts  are 
found  in  a  variety  of  conditions,  some  floating,  many  in 
damp  places,  and  many  on  the  bark  of  trees.  They  seem 
to  be  plants  that  have  barely  learned  to  live  on  land,  and 
this  change  from  the  water  to  the  land  is  one  of  the  greatest 
and  most  important  in  the  history  of  plants.  Although  in 
general  they  are  moisture-loving,  some  can  endure  great 


FIG.  160. — Ricciocarpus:  showing  thallose  body,  forked  branching,  rhizoids  on  the 
under  surface,  and  spore-cases  along  the  main  axes  (showing  position  of  archegonia). 

dryness,  so  that  the  land  habit  can  be  said  to  have  become 
well-established  among  the  liverworts. 


LIVERWORTS  167 

The  plant  body  is  flat  and  compact,  lying  prostrate  upon 
its  substratum,  and  is  often  a  thallus;  that  is,  it  shows  no 
distinction  of  stem  and  leaves,  the  whole  body  appearing 
leaf-like  (Fig.  160).  The  upper  surface  of  the  body  is 
freely  exposed  to  the  light,  but  the  lower  surface  is  against 
the  substratum  and  puts  out  hair-like  processes  (rhizoids) 
for  anchorage.  If  the  body  is  thin,  all  the  cells  contain 
chloroplasts;  but  if  the  body  is  so  thick  that  the  light 
cannot  penetrate  it,  the  under  layers  of  cells  are  not 
green. 

92.  Marchantia. — Marchantia  is  one  of  the  most  com- 
mon and  conspicuous  liverworts.  The  body  is  a  thick 


chl 


FIG.  161. — Marchantia,  cross-section  of  thallus:  showing  lower  epidermis  (from 
which,  in  other  parts  of  the  thallus,  rhizoids  are  developed),  two  layers  of 
colorless  cells  (p),  and  one  large  air-chamber  («,  a,  the  bounding  walls)  contain- 
ing cells  with  chloroplasts  (chl)  and  pierced  by  a  chimney -like  air-pore  («p). — 
After  GOEBEL. 

thallus  that  forks  repeatedly,  giving  the  appearance  of 
notches  of  greater  or  less  depth  (general  habit  as  in  Fig. 
160).  The  central  axis  of  the  thallus,  or  of  a  branch,  ends 
in  the  terminal  notch,  in  the  bottom  of  which,  therefore, 
is  the  growing  tip.  The  upper  surface  of  the  Marchantia 
body  is  blocked  off  into  small  rhombic  areas,  in  the  center 
of  each  one  of  which  is  a  minute  opening  (Fig.  162). 

A  section  through  this  body  shows  its  general  structure 

(Fig.  161).     Beginning  with  the  lower  side,  there  is  seen 

first  the  layer  of  cells  forming  the  epidermis,  from  which 

the  rhizoids  and  certain  other  appendages  arise;  above  this 

12 


168 


A  TEXT-BOOK  OF  BOTANY 


epidermis  there  are  several  layers  of  colorless  cells;  above 
these  there  is  a  series  of  large  air-chambers  into  which 
project  the  curious  cells  containing  the 
chloroplasts;  and  forming  the  dome-like 
roof  of  each  air-chamber  is  the  upper 
epidermis,  pierced  by  a  single  air-pore 
in  the  center  of  the  roof  of  each  cham- 
ber. Each  air-pore  resembles  a  little 
chimney,  built  up  with  several  tiers  of 
cells.  The  rhombic  areas  seen  on  the 
surface  of  the  body  are  the  outlines  of 
the  air-chambers,  and  the  minute  open- 
ing in  the  center  of  each  is  the  air-pore 

no.  iv.-Marchantia:  &&  162)«  This  arrangement  of  cells 
rhombic  areas  on  up-  containing  chloroplasts  exposed  in  air- 
^rfTctou^iine^li"-  chambers  that  communicate  freely 

chambers),   each   one     through 
pierced    by    an    air- 
pore— After  SACHS,      air-pores 

suggests 

the  same  general  mechan- 
ism for  plant  work  as  that  B 
described  for  leaves,   with 
their   internal    atmosphere 
and  stomata  (§13). 

A  remarkable  fact  con- 
nected with  the  Marchantia 
body,  as  contrasted  with 
that  of  the  Thallophytes, 
is  that  it  produces  no 
spores.  However,  provi- 
sion for  rapid  multiplica-  FIG  163,_Marchantia:  A,  thallus  bear- 

tion    is     made     by    the     pro-  ing    little    cups    containing  reproduc- 

„  , .  tive  bodies,  and  an  antheridial  branch 

auction  ot   peculiar  repro-        ^^  its  disk)  as  weii  as  some  very 

ductive       bodies       that      are  young  antheridial  branches;  B,  section 

through  antheridial  disk,  showing  the 
developed  in    little   CUpS  O11  sunken  antheridia.— After  KNY. 


LIVERWORTS 


169 


the  back  of  the  thallus  (Fig.  163).  These  bodies  are  round 
and  flat  (biscuit-shaped)  and  many-celled,  and  falling  out 
of  the  cup  they  start  new  thallus  bodies. 

Although  the  thallus  body  produces  no  spores,  it  does 
produce  sex-organs.  In  Marchantia,  long,  erect,  stem-like 
branches  arise  from  the  thallus,  bearing  at  their  summits 
conspicuous  disks  that  contain  the  sex-organs.  The  disks 
containing  antheridia  are  lobed  or  scalloped  (Fig.  163); 
while  those  containing  the  egg-producing  organs  are  star- 
shaped  (Fig.  165).  The  two  kinds 
of  disks  are  not  found  on  the 
same  plant. 

93.  The    antheridium.  —  The 
sperm-producing  organ  is  called 
an   antheridium,   but    it    is    very 
different  from   the  antheridia  of 
the  Thallophytes.     Instead  of  be- 
ing a  single  cell,  it  is  a  stalked, 
club-shaped  or  globular,    many- 
celled    structure   (Fig.    164).      A 
single  layer    of    cells    forms  the 
covering,  and  within  it   there  is 
a  closely  packed   mass  of    small 
cells,   each    one    of    which    pro- 
duces a  sperm.      The    sperm   is 

a  very  small  cell  with  two  long  cilia,  and  these  small 
biciliate  sperms  are  one  of  the  distinguishing  features  of  the 
liverworts  and  their  allies. 

94.  The    archegonium. — The    egg-producing    organ    is 
called  the  archegonium,  and  it  is  very  different  from  the 
oogonium  of  the  Thallophytes.     Instead  of  being  a  single 
cell,  it  is  a  many-celled  structure,  shaped  like  a  flask  with 
a  long  neck,  and  within  the  bulbous  base  the  single  egg  is 
formed   (Fig.    165,   B,  and  Fig.    166).     To  this  neck  the 
swimming  sperms  are  attracted;  they  enter  and  pass  down 


FIG.  164. — Marchantia:  antheridi- 
um and  two  sperms.  —  After 
SACHS. 


170 


A  TEXT-BOOK  OF  BOTANY 


it,  one  of  them  fuses  with  the  egg,  and  an  oospore  is 
formed.  It  is  evident  that  fertilization  can  take  place 
only  in  the  presence  of  moisture. 


A  B 

FIG.  165. — Marchantia:  A,  thallus  bearing  archegonial 
branches  of  various  ages;  B,  section  through  portion  of 
archegonial  disk,  showing  pendant  archegonia. — After 
KNY. 


FIG.  166. — Marchan- 
tia: archegonium, 
containing  an  egg; 
sperms  seen  at  the 
mouth  of  the  neck. 
—After  KNY. 


95.  The  spore-case. 

it  begins  to  germinate; 


B 

FIG.  167. — Marchantia:  A,  spo- 
rophyte  formed  within  the 
enlarged  archegonium,  show- 
ing the  spore-bearing  (a)  and 
sterile  (6)  regions;  B,  spore- 
case  discharging  spores,  the 
sterile  region  of  the  sporo- 
phyte  having  developed  into 
a  stalk.— After  KNY. 


—As  soon  as  the  oospore  is  formed 
but  instead  of  forming  a  new  Mar- 
chantia thallus,  it  produces  a  very 
different  structure.  The  oospore 
germinates  just  where  it  was  formed, 
that  is,  in  the  bulbous  base  of  the 
archegonium;  and  there  the  new 
structure  grows.  When  it  is  fully 
developed  it  is  seen  to  consist  of  a 
terminal  spore-case  full  of  spores, 
and  a  sterile  base  (Fig.  167,  A). 
While  growing,  this  spore-case  be- 
comes anchored  in  the  Marchantia 
body  (that  is,  in  the  archegonium- 
bearing  disk)  by  the  sterile  base, 


LIVERWORTS  171 

and  absorbs  the  necessary  nourishment  from  it.  When 
ripe,  the  spore-case  is  ruptured  (Fig.  167,  B),  and  the  light 
spores  are  scattered;  and  when  they  germinate  they  pro- 
duce new  thallus  bodies. 

96.  Alternation  of  generations. — The  life-history  of  Mar- 
chantia  shows  a  distinct  alternation  of  generations,  and 
since  this  is  a  feature  of  all  the  higher  plants  it  is  necessary 
to  understand  it  clearly.  The  thallus  body  produces  no 
spores,  but  produces  sperms  and  eggs;  that  is,  it  produces 
gametes,  and  hence  is  called  a  gametophyte,  which  means  a 
"gamete  plant."  The  gametes  produce  an  oospore;  but 
the  oospore  does  not  produce  a  new  thallus  plant,  producing 
instead  a  spore-case.  This  structure,  called  the  spore-case, 
does  not  produce  gametes,  but  produces  spores;  and  hence 
it  is  called  a  sporophyte,  which  means  a  "spore  plant." 
Thus  in  the  life-history  of  Marchantia  and  of  all  higher 
plants,  there  is  an  alternation  of  gametophyte  and  sporo- 
phyte. It  is  evident  that  in  this  alternation  of  generations 
the  gametophyte  is  the  sexual  and  the  sporophyte  is  the 
sexless  generation.  Therefore,  oospores  are  produced  by  the 
gametophyte,  and  ordinary  spores  by  the  sporophyte;  but 
the  oospores  always  produce  sporophytes,  and  the  ordinary 
spores  always  produce  gametophytes.  These  relations  may 
be  indicated  clearly  by  the  following  formula,  in  which  G 
and  S  are  used  for  gametophyte  and  sporophyte  respec- 
tively: 

G  I  ~OS>— S— o— G  \  ~~°^;o—S—o—G,  etc. 

(  — o  /  (  — o/ 

The  formula  indicates  that  the  gametophyte  produces 
two  gametes,  which  fuse  to  form  an  oospore,  which  produces 
the  sporophyte,  which  produces  an  ordinary  spore,  which 
produces  a  gametophyte,  etc.  It  will  be  remembered  that  a 
similar  alternation  of  generations  was  noted  in  the  red 
Algae  (§  75)  and  in  the  mildews  (§  82)  among  the  Thallo- 


172 


A  TEXT-BOOK  OP  BOTANY 


phytes,  but  it  is  not  definite  and  universal  until  the  liver- 
worts are  reached. 

It  is  important  to  note  that  in  this  life-history  the  pro- 
tected stage  of  the  plant,  that  is,  the  stage  which  can  endure 
the  winter,  is  not  a  heavy-walled  oospore,  as  is  common 
among  the  Thallophytes,  but  the  spore-case  or  sporophyte. 

97.  Other  Marchantia  forms. — Associated  with  Marchan- 
tia  are  other  liverworts  that  are  much  simpler,  and  which 
are  really  better  to  study  if  they  are  available.     They  differ 
in  having  thallus  bodies  thinner,  and  hence  simpler,  in 
structure;  in  having  the  sex-organs  directly  upon  the  thallus 
or  embedded  in  it;  and  in  having  simpler  and  more  easily 
observed  spore-cases  or  sporophytes.* 

98.  Jungermannia  forms. — These  are  commonly  called 
the  leafy  liverworts,  and  they  are  by  far  the  largest  group 
of  liverworts.     They  grow  in  damp   places;  or  in  drier 

situations  on  rocks, 
ground,  logs,  or  tree 
trunks;  or  in  the 
tropics  on  the  leaves 
of  forest  plants. 
They  are  general- 
ly delicate  plants, 
and  resemble  small 
mosses,  many  of 
them  being  com- 
monly mistaken  for 
mosses. 

The  common  name  of  the  group  suggests  one  of  its 
principal  features.  The  lowest  forms  have  a  very  simple 
thallus  body  (Fig.  168,  A);  but  in  most  of  the  forms  the 
body  consists  of  a  central  stem-like  axis  bearing  two  rows 


FIG.  168. — Jungermannia   forms:  A,  thallose  form; 
B,  leafy  form. 


*  In  case  either  Ricdocarpus  or  Riccia  can  be  obtained,  it  should  be 
studied  rather  than  Marchantia. 


LIVERWORTS 


173 


of  small,  often  crowded  leaves  (Fig.  168,  B).  There  are 
really  three  rows  of  leaves,  but  the  third  is  against  the 
substratum  and  is  usually  so  much  changed  in  appearance 
as  not  to  resemble  the  other  rows. 

There  is,  of  co.urse,  the  same  alternation  of  generations  as 
in  the  Marchantia  forms,  but  the  sporophyte  is  more  than 
a  spore-case.  It  develops  a  distinct  stalk  or  stem  that 
bears  a  spore-case  at  its  summit,  and  therefore  the  sporo- 
phyte has  become  more  complex.  Besides,  the  spore-case 
does  not  burst  open  somewhat  irregularly,  as  in  the  Mar- 
chantia forms,  but  splits  into  four  pieces  that  spread  apart 
and  expose  the  spores. 

99.  Anthoceros  forms. — This  group  contains  compara- 
tively few  forms;  but  they  are  of  great  interest,  since  many 
suppose  that  they  are  the  liverworts  that  approach  most 
nearly  the  higher  plants.  The 
thallus  body  is  very  simple,  not 
becoming  so  thick  as  are  the 
Marchantia  bodies,  nor  becoming 
leafy  bodies  as  are  those  of  the 
leafy  liverworts. 

The  important  feature  of  the 
group  is  the  sporophyte.  At  the 
"fruiting"  period  the  thallus  be- 
comes more  or  less  covered  by 
structures  that  look  like  small, 
erect  grass-blades  (Fig.  169). 
Each  of  these  blade-like  bodies 
is  a  sporophyte  that  has  devel- 
oped from  an  oospore  lying  ^m 
within  an  archegonium.  The  sporophyte  has  a  large 
bulbous  base  embedded  in  the  simple  thallus,  and  above 
this  base  there  arises  a  long  pod-like  spore-case.  The 
cells  forming  the  wall  of  this  spore-case  contain  chloro- 
plasts,  so  that  the  sporophyte  is  able  to  make  food  for  itself, 


FIG.  1 69.  —  A  rdhoce- 
ros:  A ,  thallus  with 
spore  -  cases  (spor- 
ophytes);  B,  a  sin- 
gle spore-case,  hav- 
ing split  for  the  dis- 
charge of  spores. 


174  A  TEXT-BOOK  OF  BOTANY 

in  addition  to  absorbing  food  from  the  thallus  through  the 
bulbous  base.  In  the  other  liverworts  the  sporophyte  is 
entirely  dependent  upon  the  gametophyte  for  its  food; 
but  in  the  Anthoceros  forms  the  sporophyte,  by  developing 
green  tissue,  has  begun  to  be  somewhat  independent. 

Another  important  feature  of  the  sporophyte  of  this 
group  is  that  it  continues  to  increase  in  length  like  a  stem, 
but  the  growth  takes  place  at  the  bottom  of  the  spore-case. 
As  the  pod-like  spore-case  splits  into  two  valves,  beginning 
at  the  top,  the  ripe  spores  above  are  first  exposed  and  scat- 
tered; as  the  splitting  becomes  deeper  the  region  of  the 
younger  spores  is  reached;  and  so  on  until  the  capsule  has 
become  completely  split,  and  all  the  spores  have  been  ex- 
posed (Fig.  169,  B). 

It  is  evident  that  the  Anthoceros  forms  have  the  most 
complex  sporophytes  among  liverworts.  In  addition  to 
producing  spores,  these  sporophytes  have  a  bulbous  absorb- 
ing base  and  develop  green  tissue  for  the  manufacture  of 
food. 


CHAPTER  IX 

MOSSES 

100.  General  character. — Mosses  are  very  abundant  and 
^amiliar    plants    that    occur    almost    everywhere.     They 
grow  in  all  conditions  of  moisture,  from  submerged  to  very 
dry.     Many  of  them  can  endure  drying  out  wonderfully; 
and  hence  they  can  grow  in  very  much  exposed  situations, 
as  do  many  lichens.     In  fact,  lichens  and  mosses,  being 
able  to  grow  in  the  most  exposed  situations,  are  the  first 
plants  to  appear  upon  bare  rocks  and  ground,  and  are  the 
last  plants  one  sees  in  climbing  high  mountains  or  in  going 
into  very  high  latitudes. 

Mosses  have  great  power  of  vegetative  multiplication, 
new  leafy  branches  putting  out  from  old  ones  indefinitely, 
thus  forming  thick  carpets  and  masses.  Bog  mosses  often 
completely  fill  up  bogs  or  small  ponds  and  lakes  with  a  dense 
growth,  which  dies  below  and  continues  to  grow  above  so 
long  as  the  conditions  are  favorable.  These  quaking  bogs 
or  "mosses/'  as  they  are  sometimes  called,  furnish  very 
treacherous  footing  unless  rendered  firmer  by  other  plants. 

101.  Peat. — In  moss-filled  bogs  the  water  and  the  dense 
vegetation  shut  off  the  lower  strata  of  moss  from  complete 
decay;  and  they  become  modified  into  a  coaly  substance 
called  peat,  which  may  accumulate  to  considerable  thickness 
by  the  continued  upward  growth  of  the  mass  of  moss. 
Other   marsh   plants   are   associated   with   mosses  in   the 
formation   of  peat,   and  often   the   preservation   of  these 
plants  is  remarkable.     In  fact,  the  water  of  peat-bogs  is 

175 


176 


A   TEXT-BOOK  OF  BOTANY 


antiseptic,  and  in  such  bogs  there  are  often  found  almost 
perfectly  preserved  specimens  of  ancient  trees  or  their  parts 
and  sometimes  of  mired  animals. 

Peat  is  extensively  used  for  fuel,  being  cut  into  bricks 
and  allowed  to  dry.  The  less  decomposed  peat  is  brown, 
and  the  more  completely  decomposed  is  nearly  black.  It 
is  not  formed  to  any  large  extent  in  warm  countries, 
probably  on  account  of  the  rapid  decay  of  vegetation;  but 
in  the  cooler  parts  of  the  globe  it  has  been  formed  in  very 
large  masses.  All  through  northern  Asia  and  Europe,  and 
in  the  northern  United  States  and  Canada,  there  are  millions 
of  acres  of  peat;  but  little  use  has  been  made  of  it  yet  in  the 

United  States.  Its  ex- 
tensive use  in  Ireland  is 
well  known,  but  there  it 
is  more  apt  to  be  called 
turf  than  peat. 

102.  Life-history  of  a 
Moss. — The  conspicuous 
part  of  an  ordinary  moss 
plant  consists  of  a  more 
or  less  erect  and  usually 
branching  stem  bearing 
numerous  delicate  leaves 
(Fig.  170,  A).  This  plant 
is  evidently  able  to  make 
its  own  food,  and  it  is 
anchored  to  its  substra- 
tum by  hair-like  rhi- 
zoids.  Its  power  of  vege- 
tative propagation  has 
been  described,  but  it 
produces  no  spores.  At 
certain  times,  however,  there  usually  appears  at  the  end  of 
the  main  stem  or  at  the  end  of  a  branch  a  rosette  of 


FIG.  170. — An  ordinary  moss  plant,  showing 
the  leafy  stem  (A)  with  its  rhizoids,  and 
a  rosette  (B)  containing  sex-organs. 


MOSSES 


177 


leaves  (Fig.  170,  5),  often  called  the  moss  flower.  In  the 
center  of  this  rosette  there  is  a  group  of  antheridia  and 
archegonia,  sometimes  both  kinds  of  organs  in  a  single 
rosette,  sometimes  only  one  kind. 

The  antheridia  are  club-shaped  organs  containing  nu- 
merous biciliate  sperms  (Fig.  171,4);  and  the  archegonia 


FIG.  171. — Sex-organs  of  a  moss:  A, an  antheridium  discharging  a  mass  of  mother- 
cells  (a)  containing  sperms,  and  also  a  single  enlarged  mother-cell  (fc)  and  sperm 
(c);  B,  a  group  of  archegonia  within  a  rosette  of  leaves;  C,  an  archegonium. — 
After  SACHS. 

are  flask-shaped  organs  usually  with  very  long  necks,  and 
containing  a  single  egg  in  the  bulbous  base  (Fig.  171,  B 
and  C).  These  sex-organs  are  exactly  like  those  described 
for  liverworts  (§§93  and  94).  It  is  evident  that  this  leafy 


178 


A  TEXT-BOOK  OF  BOTANY 


moss  plant,  which  does  not  produce  spores,  but  which  does 
produce  sex-organs,  is  the  gametophyte  generation  in  the 
life-history.     It  is  plain  that  the  ciliated  sperms  are  organ- 
ized for  swimming,  and  that  fertili- 
zation can  take  place  only  when  there 
is  sufficient  moisture  for  this  purpose. 


FIG.  172. — Developing  sporophyte  of  a  moss:  A ,  young 
sporophyte  developed  from  egg  in  archegonium; 
B  and  C,  more  advanced  stages,  in  which  the 
sporophyte  is  elongating  and  becoming  anchored 
in  the  leafy  plant. — After  GOEBEL. 


FIG.  173. — A  common  moss- 
bearing  mature  sporo- 
phytes,  which  are  long- 
stalked  spore  -  cases.  — 
After  SCHENCK. 


MOSSES 


179 


It  must  be  remembered,  however,  that  the  sperms  are  very 
small  and  can  swim  in  such  a  film  of  water  as  may  be  left 
on  the  plant  by  a  heavy 
dew  or  rain.  Since  many 
mosses  grow  in  very  dry 
places,  fertilization  with 
them  must  be  very  in- 
frequent. When  the 
sperms  are  free  to  swim 
they  are  attracted  toward 
the  necks  of  the  arche- 
gonia,  pass  down  them, 
reach  the  egg,  and  fertili- 
zation is  accomplished. 

The  oospore  thus  formed  within  the  archegonium  at 
once  begins  to  germinate  (Fig.  172),  and  forms  the  spore- 
producing  structure,  which  in  mosses  is  much  more  than  a 


FIG.  174.— Spore-cases  of  a  moss,  from  which 
the  lids  have  fallen,  displaying  the  teeth. 
— After  KERNER. 


IIG.  175. — Filamentous  growth  of  the  young  moss:  A,  very  young  filament  coming 
from  a  spore  («);  B,  older  filament,  showing  branching  habit,  remains  of  old 
spore  («),  rhizoids  (r),  and  buds  (6)  which  develop  the  erect  leafy  branches. — 
After  MUELLER-THURGAU. 


180  A   TEXT-BOOK  OF  BOTANY 

spore-case.  It  has  a  long  slender  stalk,  which  becomes 
anchored  in  the  stem  of  the  leafy  plant  (Fig.  172);  and  the 
stalk  bears  an  elaborate  and  usually  urn-shaped  spore-case 
full  of  spores  (Fig.  173).  This  spore-case  opens  by  means 
of  a  lid,  which  drops  off;  and  often  at  the  mouth  of  the 
urn  thus  opened  there  may  be  seen  a  set  of  delicate  teeth 
extending  from  the  margin  of  the  rim  and  meeting  in  the 
center  (Fig.  174).  These  teeth  bend  inward  and  outward 
as  they  are  dry  or  moist,  and  help  discharge  the  spores. 
It  is  evident  that  this  -spore-case  with  its  anchored  stalk  is 
the  sporophyte  generation  in  the  life-history. 

When  the  spores  fajl  in  suitable  situations  they  germi- 
nate, and  each  one  produces  a  green  branching  filament 
that  looks  like  one  of  the  filamentous  green  Algae  (Fig. 
175).  This  branching  filamentous  growth  spreads  over  the 
substratum,  and  presently  there  appear  upon  it  buds 
(Fig.  175,  B,  b),  each  of  which  develops  an  erect  leafy  stem, 
which  is  recognized  as  a  new  leafy  moss  plant,  the  form 
with  which  this  account  of  the  life-history  was  begun. 

103.  Alternation  of  generations* — In  the  life-history  just 
given,  it  is  evident  that  the  prostrate  green  filament  and 
the  erect  leafy  stems  are  two  parts  of  the  gametophyte; 
for  the  leafy  stems  simply  arise  as  erect  branches  from  the 
prostrate  filament.  It  is  strictly  true,  therefore,  that  the 
so-called  moss  plant,  the  conspicuous  part  of  the  moss,  is 
a  leafy  branch  of  the  gametophyte.  These  leafy  branches 
become  independent  of  the  filament  by  sending  out  rhizoids 
into  the  substratum,  so  that  it  is  only  by  actually  germina- 
ting the  spores  that  the  filaments  are  seen.  Not  only  does 
this  branch  bear  leaves,  and  hence  perform  the  chief  work 
of  food  manufacture,  but  it  also  bears  the  sex-organs. 

The  sporophyte,  on  the  other  hand,  is  dependent  upon 
this  leafy  branch  for  its  food-supply,  and  in  that  sense  may 
be  said  to  be  parasitic  upon  it.  Its  only  work  is  to  produce 
spores;  while  the  gametophyte  does  the  chlorophyll  work 


MOSSES  181 

and  also  produces  the  sex-organs.     The  life-history,  with 
its  alternating  generations,  may  be  indicated  as  follows: 


etc. 

104.  The  great  groups  of  Mosses.  —  There  are  two  great 
groups  of  mosses,  knowj^uni,  lllU  tog^nosses  and  the  true 
mosses.  The  bog  m^SS^^apge^k/flj^ailkd  mosses  found 
abundantly  in  bo^s^id  marshy  ground,  arm  are  the  most 
conspicuous  peapformers.  They.dtffef-fro'mjhe  true  mosses 
in  structure  inunafn^'ways  that  need  rwpbe  mentioned, 
but  one  contrastHcchrato^ttention.  When 


the  spore  of  a  bog  mSStf^ggjaaBiee&s^it,  does  not  produce  a 
branching  green  filament,  but  a  flat  compact  thallus  body 
like  that  of  the  liverworts.  On  this  thallus  body  the 
erect  leafy  branches  arise,  just  as  they  do  from  the  fila- 
mentous body  in  true  mosses.  This  is  interesting,  because 
in  the  bog  mosses  the  thallus  body  of  the  liverworts  is 
continued,  and  also  because  it  indicates  that  the  prostrate 
filamentous  body  of  the  true  mosses  is  probably  a  modified 
thallus  body. 

The  true  mosses  are  much  more  numerous  than  the  bog 
mosses,  and  live  in  a  far  greater  variety  of  situations. 
Some  of  them  are  also  peat  formers,  but  most  of  them  have 
become  established  in  much  drier  situations. 

105.  The  erect  leafy  axis.  —  The  lowest  green  plants  live 
in  the  water  or  in  very  moist  places,  but  the  liverworts 
begin  to  occupy  the  land.  In  this  new  position  they  are 
better  exposed  to  light,  which  is  an  advantage  in  food 
manufacture;  but  they  are  in  danger  of  being  dried  out  by 
the  air.  In  consequence  of  these  dangers,  various  protect- 
ive structures  have  been  developed,  one  of  the  first  being  a 
compact  body  with  an  epidermis.  An  exposure  of  more 
green  tissue  to  the  light  is  secured  by  the  leafy  liverworts 
in  their  development  of  leaves,  but  their  bodies  are  prostrate 


182  A  TEXT-BOOK  OF  BOTANY 

and  the  best  exposure  is  not  obtained.  The  mosses  have 
made  still  further  progress  in  developing  an  erect  branch 
upon  which  leaves  are  spread  out  to  the  light  and  air  freely 
in  all  directions.  All  this  advance  has  been  made  by  the 
gametophyte,  which  in  the  mosses  has  reached  the  best 
position  for  leaves  and  hence  for  food  manufacture.  How 
progress  in  this  direction  is  carried  further  by  the  higher 
plants  will  be  seen  in  subsequent  chapters. 


CHAPTER  X 

FERNS 

106.  Summary. — Before  studying  the  ferns,  it  is  well  to 
note  the  progress  that  has  been  made  by*  the  plants  previ- 
ously considered.  It  has  been  said  that  the  Alga?  and 
Fungi  together  form  the  first  great  division  of  the  plant 
kingdom,  the  Thallophytes.  The  liverworts  and  mosses 
together  form  the  second  great  division,  called  the  Bryo- 
phytes,  a  name  meaning  "moss  plants. "  The  ferns  intro- 
duce the  third  great  division,  called  the  Pteridophytes,  which 
means  "fern  plants."  A  summary  of  the  contributions 
made  by  the  Bryophytes  to  the  progress  of  plants  is  as 
follows: 

(1)  The  land  habit. — The  Bryophytes  establish  green 
plants  upon  the  land,  and  as  a  consequence  begin  to  develop 
those  structures  that  the  new  conditions  demand. 

(2)  Alternation  of  generations. — A  life-history  consisting 
of  alternating  sexual   (gametophyte)   and  sexless  (sporo- 
phyte)  generations  is  finally  established,  although  it  is  in- 
dicated in  the  life-histories  of  certain  Thallophytes. 

(3)  Gametophyte  the  chlorophyll  generation. — In  the  alter- 
nation the  gametophyte  generation  develops  the  chloro- 
plasts  for  food  manufacture,  and  on  this  account  is  the  con- 
spicuous generation.    When  a  moss  or  a  liverwort  is  spoken 
of,  therefore,  the  gametophyte  is  usually  referred  to. 

(4)  Sporophyte  dependent. — The  sporophyte  in  the  Bry- 
ophytes is  dependent  upon  the  gametophyte  for  food,  and 
hence  remains  attached  to  it.    Only  by  the  Anthoceros  forms 
has  a  partial  independence  of  the  sporophyte  been  attained. 

13  183 


184 


A  TEXT-BOOK  OF  BOTANY 


(5)  Appearance  of  leaves. — Among  the  Bryophytes  very 
simple  leaves  are  developed  by  the  gametophyte,  and  the 
mosses  produce  leaves  upon  an  erect  stem. 

(6)  Many-celled  sex-organs. — The  many-celled  antheridia 
and  flask-shaped  archegonia  are  very  characteristic  of  Bryo- 
phytes, and  distinguish  even  the  thallose  forms  from  any 
Thallophytes. 

107.  General  characters  of  Ferns. — The  ferns  are  well- 
known  plants,  and  the  ordinary  forms  are  easily  recognized 


FIG.  176.— Shield  ferns. 


(Fig.  176).  In  fact,  the  general  appearance  of  the  large 
compound  leaves  is  so  characteristic  that  when  a  leaf  is  said 
to  be  fern-like  a  particular  appearance  is  suggested.  Al- 


•i 


185 


186 


A  TEXT-BOOK  OF  BOTANY 


though  ferns  are  found  in  considerable  numbers  in  temper- 
ate regions,  their  chief  display  is  in  the  tropics,  where  they 
form  a  striking  and  characteristic  feature  of  the  vegetation. 
In  the  tropics  not  only  are  great  masses  of  the  low  forms 
to  be  seen,  from  those  with  delicate  and  filmy  moss-like 
leaves  to  those  with  huge  leaves,  but  also  tree  forms  with 


FIG.   178.— The  staghorn  fern,  which  is  an  epiphyte. 

cylindrical  trunks  encased  by  the  rough  remnants  of  fallen 
leaves  and  sometimes  rising  to  a  height  of  thirty-five  to 
forty-five  feet,  with  a  crown  of  great  leaves  fifteen  to 
twenty  feet  long  (Fig.  177).  There  are  also  air  forms 
(Fig.  178),  that  is,  ferns  that  perch  upon  other  plants  but 


FERNS 


1ST 


derive  no  nourishment  from  them  (§  41).  This  habit  be- 
longs chiefly  to  the  moist  tropics,  where  plants  may  obtain 
sufficient  moisture  from  the  air  without  sending  roots  into 
the  soil. 

108.  Sporophytes. — If  an  ordinary  fern  be  examined,  it 
will  be  discovered  that  it  has  a  horizontal  underground 
stem  or  rootstock  (§  27),  which 
sends  out  roots  into  the  soil,  and 
one  or  more  large  leaves  into 
the  air  (Fig.  179).  These  leaves, 
appearing  to  come  directly  from 
the  soil,  were  once  supposed  to 
be  different  from  ordinary  leaves 
and  were  called  fronds  ;  but  al- 
though the  name  is  still  used  in 
connection  with  fern  leaves,  it 
is  neither  nec- 
essary nor  ac- 
curate. These 
leaves  are  usu- 
ally compourd, 
branchingeith- 
er  pmnately  or 


i.    179.— The    habit    of   an   ordinary  fern 
showing  the  horizontal  rootstock  sending  out  roots  and 

rpi  leaves,  and  also  the  peculiar  rolled  tip  of  the  developing 

leaves. 

two  peculiari- 
ties about  fern  leaves  that  should  be  noted.  One  is  that 
in  expanding  the  leaves  seem  to  unroll  from  the  base,  as 
though  they  had  been  rolled  from  the  apex  downward,  the 
apex  being  in  the  center  of  the  roll.  When  unrolling,  this 
gives  the  leaves  a  crozier-like  tip  (Fig.  179).  The  other 
peculiarity  is  that  the  veins  fork  repeatedly  (Fig.  180). 
This  combination  of  unrolling  leaves  and  forking  veins  is 
very  characteristic  of  ferns. 

Probably  the  most  important  fact  about  the  fern  body 


188 


A   TEXT-BOOK   OF   BOTANY 


is  that  it  contains  a  vascular  system  (§  24)  (Fig.  181). 
The  appearance  of  this  system  marks  some  such  epoch  in 
the 'evolution  of  plants  as  is  marked  among  animals  by  the 
appearance  of  the  backbone.  As  animals  are  often  grouped 
as  vertebrates  and  invertebrates,  so  plants  are  often 
grouped  as  vascular  plants  and  non-vascular  plants,  the 
latter  being  the  Thallophytes  and  the  Bryophytes,  the  for- 
mer the  ferns  and  the  seed-plants.  The  presence  of  this 
vascular  system  means  a  special  conducting  system,  and 
in  connection  with  it  there  are  developed  the  first  roots 


FIG.  180.— Portion  of  the  leaf  of  maidenhair  fern,  showing  the  forking  veins. 

and  the  first  complex  leaves.  Such  a  plant  body,  with  its 
vascular  system  and  roots  and  complex  leaves,  is  so  dif- 
ferent from  any  plant  body  among  Bryophytes  that  the 
greatest  gap  in  the  whole  series  of  plants,  from  lowest  to 


FERNS  189 

highest,  is  felt  to  be  the  one  between  Bryophytes  and 
Pteridophytes.  On  account  of  the  vascular  system  and 
other  resistant  structures,  the  remains  of  ferns  have  been 


FIG.  181. — Cross-section  of  the  stem  (rootstock)  of  a  fern,  showing  the  peculiar 
vascular  axis,  the  large  xylem  vessels  being  completely  surrounded  by  the 
phloem. 

preserved  in  great  abundance  in  the  rocks.  These  records 
show  that  the  ferns  are  a  very  ancient  group,  occurring 
in  special  abundance  during  the  Coal-measures. 

Another  striking  fact  about  this  leafy  body  of  the 
ferns  is  that  it  never  produces  sex-organs,  but  does  produce 
spores  abundantly.  This  means  that  it  is  the  sporophyte 
in  the  life-history  of  the  fern,  and  when  it  is  contrasted 
with  the  sporophyte  of  Bryophytes  the  differences  are 
remarkable.  Among  the  liverworts  and  the  mosses  the 
sporophyte  is  a  leafless  structure  attached  to  the  gameto- 
phyte  and  dependent  on  it,  while  the  gametophyte  is  the 
leafy  body  doing  chlorophyll  work.  Among  the  ferns, 
however,  the  sporophyte  is  an  elaborate  leafy  structure 
and  entirely  independent.  Therefore,  when  one  ordinarily 


190 


A  TEXT -BOOK  OF  BOTANY 


speaks  of  a  moss  and  a  fern,  the  gametophyte  is  referred 
to  in  the  former  case  and  the  sporophyte  in  the  latter. 
This  means  that,  in  passing  from  mosses  to  ferns,  plants 
have  transferred  the  chief  work  of  food  manufacture  from 
the  gametophyte  to  the  sporophyte,  which  has  thus  become 
the  conspicuous  generation.  The  leaves  of  mosses,  there- 
fore, are  gametophyte  leaves;  while  the  leaves  of  ferns  are 
the  first  sporophyte  leaves.  A  common  and  brief  statement 
of  the  contrast  between  the  two  groups  is  that  mosses  have 
a  leafless  and  ferns  a  leafy  sporophyte.  How  the  leafless 
sporophyte  has  become  a  leafy  one  is  an  interesting  but  un- 


A  B 

FIG.  182. — Sporangia  of  ferns:  .A,  elongated  sori,  with  pocket-like  indusia;  B,  round 
sori,  with  shield-like  indusia. 


FERNS 


191 


answered  question.  The  great  interest  of  the  Anthoceros 
forms  (§  99)  is  due  to  the  fact  that  their  sporophytes  are 
green  and  do  chlorophyll  work;  and  this  has  suggested  the 
thought  that  from  such  green  tissue  leaves  have  been  de- 
veloped, and  thus  a  leafy  sporophyte  has  been  started. 

109.  Sporangia. — Upon  the  under  surface  of  fern 
leaves  dark  dots  or  lines  are  often  seen  (Fig.  182).  These 
arc  groups  of  sporangia,  usu- 
ally occurring  along  the  veins 
of  the  under  surface,  but  some- 
times in  long  lines  along  the 
edge,  the  margin  of  the  leaf 
rolling  in  and  protecting  them, 
as  iii  maidenhair  fern  and  com- 
mon brake  (Fig.  183).  In  ferns 
having  the  groups  of  sporangia 
away  from  the  margin,  each 
group  (sorus)  is  usually  pro- 
tected by. a  delicate  flap  (indu- 
fiium)  growing  out  from  the  epi- 
dermis, sometimes  forming  a 
pocket  (Fig.  182,  ^4.)  and  some- 
times an  umbrella-like  or  shield- 
like  covering  (as  in  shield  ferns) 
(Fig.  182,  £).  The  position  and 
the  shape  of  the  sorus  and  the  character  of  the  indusium 
furnish  useful  characters  in  the  classification  of  ferns. 

Most  fern  leaves  do  chlorophyll  work  and  produce 
sporangia,  two  very  distinct  kinds  of  work.  In  some 
ferns,  however,  some  of  the  leaves  are  sterile,  that  is,  do 
not  produce  sporangia,  the  other  leaves  doing  both  kinds 
of  work;  while  in  other  ferns  certain  leaves  or  leaf  branches 
are  set  apart  to  produce  sporangia  and  do  no  chlorophyll 
work,  and  vice  versa,  the  two  kinds  of  work  thus  being 
divided  among  the  leaves  or  leaf  branches.  Such  a 


FIG.  183. — Sporangia  of  ferns,  show- 
ing marginal  lines  of  sporangia 
protected  by  the  inrolled  margin 
of  the  leaf:  A ,  the  common  brake; 
B,  maidenhair  fern. 


192 


A  TEXT-BOOK  OF  BOTANY 


division  of  work  occurs  in  the  royal  fern,  climbing  fern, 
ostrich  fern,  sensitive  fern,  moonwort  (Fig.  184),  adder's 
tongue,  etc. 

The  sporangium  of  an  ordinary  fern  consists  of  a  spore- 
case  with  a  slender  stalk  (Fig.  185).  The  case  has  a  del- 
icate wall  formed  of  a  single  layer  of  cells; 
and,  extending  around  it  from  the  stalk  and 
nearly  to  the  stalk  again,  like  a  meridian 
line  about  a  globe,  is  a  row  of  peculiar  cells 


FIG.  185.— Section  through  the  sorus  of  a  shield  fern,  showing  in- 
dusium  and  sporangia. — After  ENGLER  and  PRANTL. 

with    thick   walls,   forming    a    heavy   ring. 
This  ring  is  like  a  bent  spring;   and  when 
the  delicate  wall  begins  to  yield,  the  spring 
straightens  violently,  the  wall  is  torn,  and 
FIG.  184 —Am     -   as  ^e  sPrmg  rebounds  the  spores  are  hurled 
wort,      showing   with   considerable  force,  like   a  handful  of 
pebbles    thrown    forward    from    the    hand. 


branches  of  a  leaf.    This   discharge   of   spores  may  be  seen  by 

—  After     STRAS- 

BURGER.  placing  some  mature  sporangia  upon  a  moist 


FERNS 


193 


slide,  and  under  a  low  power  watching  them  as  they  dry 
and  burst. 

110.  Gametophytes. — In  continuing  the  life-history  of  a 
fern,  the  spores  when  discharged,  as  just  described,  begin 
to  germinate,  provided  they  have  reached  suitable  con- 
ditions. Each  germinating  spore  produces  a  green  thallose 
body  that  resembles  a  very  small  delicate  liverwort 
(Fig.  186).  It  is  deeply  notched,  having  a  general  heart- 
shaped  outline,  and 
is  usually  less 
than  one-fifth  of 
an  inch  in  diame- 
ter. This  thallus 
is  so  thin  that  all 
its  cells  contain 
chloroplasts,  and 
rhizoids  from  the 
under  surface  an- 
chor it  to  .the  soil. 
It  is  evident  that 
it  is  an  indepen- 
dent plant,  al- 
though a  very 
small  one.  Upon 
this  minute  plant 
the  sex-organs  are 

produced,  and  therefore  it  is  the  garnet ophyte  in  the  life- 
history.  This  fern  gametophyte,  because  it  is  a  thallus 
body  which  precedes  the  appearance  of  the  large  sporo- 
phyte,  has  been  called  the  prothallium  (or  prothallus), 
and  this  name  has  come  to  be  very  commonly  used  for 
gametophyte  among  all  the  higher  plants.  At  the  bottom 
of  the  conspicuous  notch  of  the  prothallium  is  the  grow- 
ing point,  representing  the  apex  of  the  plant. 

The  antheridia  and  the  archegonia  are  produced  on  the 


FIG.  186. — Gametophyte  (prothallium)  of  a  fern:  A, 
under  surface  showing  rhizoids  (rA).  antheridia  (an), 
and  archegonia  (ar);  B,  under  surface  of  an  older 
gametophyte,  showing  the  young  sporophyte,  with 
root  (w)  and  leaf  (6). — After  SCHENCK. 


194 


A  TEXT-BOOK  OF  BOTANY 


under  surface  of  the  prothallium  in  the  region  of  the  central 
axis.  When  the  prothallia  are  very  young,  the  antheridia 
begin  to  appear;  and  if  the  prothallia  are  poorly  nourished 
and  stunted  only  antheridia  appear.  In  mature,  well- 
nourished  prothallia,  however,  archegonia  also  appear.  In 
consequence  of  their  late  appearance,  the  group  of  archego- 
nia is  near  the  notch,  that  is,  near  the  growing  point,  while 
the  group  of  antheridia  is  farther  back,  on  the  older  part  of 
the  prothallium  (Fig.  186,  A). 

The  antheridia  and  the  archegonia  are  not  free  and  pro- 
jecting organs,  as  among  the  Bryophytes,  but  they  are 
more  or  less  sunken  in  the  tissue  of  the  prothallium  and 
open  on  its  surface.  In  the  case  of  the  archegonium  only 


FIG.  187. — Archegonium  of  a  fern  containing  an  egg  (e),  the  neck  being  curved  back- 
ward toward  the  antheridia. 

the  neck  projects,  and  this  is  usually  bent  backward  to- 
ward the  antheridia  (Fig.  187).  The  egg  resembles  those 
of  all  other  archegonium-bearing  plants;  but  the  sperms 
are  very  different  from  those  of  Bryophytes,  having  large 


FERNS 


195 


spirally  coiled  bodies,  blunt  behind  and  tapering  to  a  beak 
in  front,  the  beak  bearing  numerous  cilia  (Fig.  188).  The 
fern  sperm,  therefore,  is  a  large,  spirally  coiled,  multiciliate 


Fro.   188. — Two  antheridia  of  a  fern  (A),  one  containing  sperms,  the  other  discharg- 
ing them;  also  a  single  sperm  much  enlarged  (B). 


sperm,  as  compared  with  the  small  biciliate  sperm  of  Bry- 
ophytes. 

With  a  ciliated  sperm,  fertilization  can  be  effected  only 
in  the  presence  of  moisture,  and  if  prothallia  are  kept  dry 
fertilization  does  not  occur.  In  nature,  however,  the  pro- 
thallia lying  prostrate  on  the  substratum  are  in  a  favor- 
able position  for  moisture;  and  when  there  is  a  film  of  mois- 
ture between  the  prothallium  and  the  substratum  the 
sperms  can  swim  to  the  archegonia. 

The  oospore  which  is  produced  germinates  at  once  and 
forms  the  leafy  sporophyte  (Fig.  186,  B}.  The  young  stem 
and  the  root  remain  under  the  soil,  but  the  young  leaf  is 
seen  curving  upward  through  the  notch  of  the  prothallium 
and  growing  up  into  the  air  and  light.  For  a  short  time  the 
young  plantlet  absorbs  nourishment  from  the  prothallium, 
but  with  its  own  root  system  and  leaves  it  soon  becomes 


196  A  TEXT-BOOK  OF  BOTANY 

independent.  In  fact,  the  prothallium  is  so  small,  and  the 
leafy  sporophyte  becomes  relatively  so  large,  that  the 
dependence  of  the  latter  upon  the  former  is  a  very  small 
item  in  the  life-history. 

111.  Alternation  of  generations.  —  The  contrast  between 
the  alternating  generations  of  mosses  and  the  same  genera- 
tions in  ferns  is  striking.  In  mosses  the  gametophyte  is 
the  conspicuous  phase  in  the  life-history,  with  its  prostrate 
filaments  and  leafy  branches;  while  in  ferns  the  gameto- 
phyte (prothallium)  is  a  very  inconspicuous  phase  in  the 
life-history,  being  seen  only  by  those  who  know  what  to 
look  for,  and  resembling  a  very  small  simple  liverwort. 
In  the  mosses  the  sporophyte  is  at  most  only  a  stalked 
spore-case,  attached  to  the  gametophyte  and  dependent 
upon  it  for  nourishment;  while  in  ferns  the  sporophyte  is 
a  large,  independent,  leafy  plant,  with  vascular  system 
and  roots. 

The  formula  for  the  life-history  of  a  fern  may  be  written 
as  follows: 


G(prothallium)—  °>  O  —  £(leafy  plant)  —  O  —  GrH%>  O  —  S  —  O—  G, 

etc. 


CHAPTER  XI 

HORSETAILS   AND   CLUB-MOSSES 
HORSETAILS 

112.  General  characters. — The  horsetails  or  equisetums 
are  represented  to- 
day by  only  twenty- 
five  species ;  but 
during  the  Coal- 
measures  the  spe- 
cies were  very  nu- 
merous, and  some 
of  them  were  great 
trees,  forming  a 
conspicuous  part  of 
the  forest  vegeta- 
tion. They  grow 
in  moist  or  dry 
ground,  sometimes 
in  great  abun- 
dance, and  have 
such  a  character- 
istic appearance 
that  they  cannot 
be  mistaken. 

The  stem  is  slen- 
der and  conspicu- 
ously jointed,  the 

joints  Separating      FIG.  189. — Equisetum:  showing  the  jointed  and  fluted 

..  ._,.  1  QO\  stem,  the  sheath  of  minute  leaves   at  each  joint, 

easily      (r  Ig.       189) .          strobili  in  various  stages,  and  some  young  branches, 

197 


198 


A  TEXT-BOOK   OF  BOTANY 


It  is  also  green,  and  fluted  with  small  longitudinal  ridges; 
and  there  is  such  an  abundant  deposit  of  silica  in  the  epi- 
dermis that  the  plants  feel  rough.  This  last  property  sug- 
gested formerly  its  use  in 
scouring,  and  the  name 
"  scouring  rush."  At  each 
joint  there  is  a  sheath  of 
minute  leaves,  more  or  less 
coalesced,  the  individual 
leaves  sometimes  being 
indicated  only  by  minute 
teeth.  This  arrangement 
of  leaves  in  a  circle  about 
the  joint  is  the  cyclic  ar- 
rangement, the  leaves  be- 
ing said  to  be  whorled  (§8). 
These  leaves  contain  no 
chlorophyll  and  have  evi- 
dently abandoned  food 
manufacture,  which  is  car- 
ried on  by  the  green  stem; 
hence  they  are  scales  rather 
than  foliage  leaves.  The 
aerial  stem,  which  arises 
from  an  elongated  root- 
stock,  is  either  simple  or 
profusely  branched.  In 
some  cases  the  aerial  stems  early  in  the  season  are  simple, 
usually  not  green,  and  bear  the  sporangia  (Fig.  190); 
while  the  later  branches  from  the  same  rootstock  are 
sterile,  profusely  branched,  and  green  (Fig.  191). 

113.  Strobilus.— At  the  apex  of  the  aerial  stem  there 
may  be  found  a  more  or  less  conspicuous  cone-like  structure, 
called  the  strobilus,  meaning  "pine  cone,"  whrch  it  resem- 
bles in  general  outline  (Fig.  190).  The  strobilus  is  a  com- 


FIG.  190. — Early  fertile  shoots  of  Equise- 
tum,  which  are  not  green,  have  con- 
spicuous leaf -sheaths  at  the  joints,  and 
bear  conspicuous  strobili;  beginnings 
of  the  later  sterile  shoots  also  seen. 


HORSETAILS  AND   CLUB-MOSSES 


199 


pact  group  of  modified  leaves  bearing  sporangia.  Just 
as  in  some  ferns  certain  leaves  are  set  apart  to  do  chloro- 
phyll work  and  others 
to  bear  sporangia,  so  in 
the  Equisetum  the  same 
division  of  work  oc- 
curs; but  the  notable 
thing  is  that  the  spo- 
rangium-bearing leaves 
are  massed  together  in 
a  cluster  that  is  quite 
distinct  from  the  rest  of 
the  plant.  Leaves  set 
apart  for  bearing  spo- 
rangia are  called  spo- 
rophylls,  which  means 
"spore  leaves.''  A 
strobilus,  therefore,  is 
a  group  of  sporophylls 
that  form  a  more  or 
less  distinct  cluster,  dis- 
tinct from  the  rest  of 
the  plant. 

In  Equisetum  each 
sporophyll  consists  of 
a  stalk-like  portion  and 
a  shield-like  top,  be- 
neath which  the  several 
sporangia  hang  (Fig. 
192,  A).  The  spores 
have  a  very  peculiar 
outer  wall.  It  consists 
of  two  spiral  bands 

wound  about  the  spore  and  fastened  to  it  only  at  the  point 
where  they  intersect  (Fig.  192,  £).     When  dry,  the  bands 
14 


FIG.  191.— Later  sterile  shoots  of  the  species 
shown  in  Fig.  190,  and  photographed  a 
month  later. 


200 


A  TEXT-BOOK  OF  BOTANY 


B 


loosen  and  uncoil;  when  moistened,  they  close  around  the 
spore.  The  coiling  and  uncoiling  movements  of  these  bands 

as  they  are  wet 
or  dry  entan- 
gle the  spores, 
and  they  fall  in 
clumps,  a  num- 
ber of  them 
thus  germinat- 
ing close  to- 

FIG.  192. — A,  a  sporophyll  of  Equisetum,  bearing  sporangia      pother 
beneath  the  shield-like  top;  B  and  C,  spores,  showing 
the  unwinding  of  the  two  bands  forming  the  outer  coat.  114.    GametO- 

phyte.  —  When 

the  spores  of  an  Equisetum  germinate  they  give  rise  to 
gametophytes  that  in  all  general  features  resemble  those  of 
the  ferns;  that  is,  they  are  small,  green  thallus  bodies  pro- 
ducing antheridia  and  archegonia.  From  the  oospores  pro- 
duced in  the  archegonia  the  large  sporophyte  arises,  with 
its  roots,  xootstock,  branches,  leaves,  and  strobili. 

It  is  evident  that,  although  an  Equisetum  does  not 
seem  to  resemble  a  fern  in  the  least,  the  life-history  and 
the  character  of  the  alternating  generations  are  the  same. 

CLUB-MOSSES 

115.  General  characters. — The  club-mosses  often  look 
like  coarse  mosses,  as  the  name  suggests.  Some  of  the 
larger  ones  are  called  also  ground  pines,  because  of  a  cer- 
tain resemblance  to  miniature  pines.  They  are  slender 
branching  plants,  with  the  prostrate  or  erect  stems  com- 
pletely clothed  with  small  leaves  (Fig.  193).  The  larger 
and  coarser  forms  are  abundant  in  the  Northern  woods,  the 
prostrate  stems  often  trailing  extensively  and  giving  rise  to 
erect  branches.  The  more  delicate  forms  are  abundant 
in  the  tropics,  and  are  very  common  in  greenhouses  as 
decorative  plants. 


HORSETAILS  AND   CLUB-MOSSES 


201 


During  the  Coal-measures  the  club-mosses  occurred  in 
great  abundance,  and  among  them  were  large  trees  of  vari- 
ous kinds,  forming  a  very  prominent  part  of  the  forest 


B 


FIG.  193.—Lycopodium:  A,  the  whole  plant,  showing  the  horizontal  stem  giving 
rise  to  roots  and  erect  branches  bearing  strobili;  B,  a.  single  sporophyll  with  its 
sporangium;  C,  spores  much  magnified. — After  WOSSIDLO. 

vegetation.     As  in  the  case  of  the  equisetums,  therefore, 
the  club-mosses,  or  Lycopods  as  they  are  called,  were  once 


202 


A  TEXT-BOOK  OF  BOTANY 


far  more  conspicuous  plants  than  they  are  now,  and  only 
the  smaller  forms  have  persisted  to  the  present  time. 

116.  Strobili. — One  of  the  conspicuous  features  of  the 
lycopods  is  the  cylindrical  strobilus,  which  usually  termi- 
nates the  erect  branches,  and  is  the  "club"  that  enters  into 
the  name  club-moss  (Fig.  193,  A).  Sometimes  the  strobilus 
is  quite  distinct  from  the  rest  of  the  stem;  and  sometimes  it 
cannot  be  distinguished  from  it,  so  that  there  is  no  external 
indication  where  leafy  stem  ends  and  strobilus  begins. 

The  leaves  of  the  strobilus  resemble  the  ordinary  fo- 
liage leaves;  but  each  one  is  a  sporophyll,  bearing  a  single 
large  sporangium  on  its  upper  surface  at  the  base  (Fig.  193, 

B),  so  that  the  sporangium  ap- 
pears in  the  axil  of  the  sporo- 
phyll. Among  the  ferns  the  spo- 
rangia are  numerous  on  the  under 
side  of  leaves;  among  equisetums 
they  are  several  on  the  under  side 
of  sporophylls;  among  lycopods 
they  are  solitary  on  the  upper 
side  of  sporophylls. 

117.  Lycopodium. — The  Lyco- 
podium  forms  are  chiefly  the 
coarse  club-mosses  of  temperate 
regions,  and  are  mostly  spoken  of 
as  the  large  club-mosses.  The 
strobili  are  often  conspicuous  and 
very  distinct  from  the  rest  of 
the  plant.  This  leafy,  branching 
plant  with  its  strobili  is,  of  course, 
the  sporophyte  (Fig.  193,  A). 
When  its  spores  germinate  they 

rkrnr|nr»0  o-arnAf  nrJiirf  AC  •  Vmf  fVi^GA 
PF<  3  gametOpnyteS,  t 

instead     of    being 
sou.— After  BRUCHMANN.        green,    prostrate,   thallose   bodies, 


FIG.    194. — Subterranean    gam- 
etophytes     of     Lycopodium, 
showing   their  irregular,   tu- 
berous form;  the  dotted  line     frametophvtes 
represents  the  surface  of  the     * 


HORSETAILS  AXD  CLUB-MOSSES 


203 


as  are  the  gametophytes  (prothallia)  of  ferns  and  equi- 
setums,  are  subterranean  tuberous  bodies  with  no  chloro- 
phyll, on  which  the  antheridia  and  archegonia  appear  (Fig. 
194).  In  some  forms  of  Lycopodium  the  tuberous  prothal- 
lium  develops  an  aerial  portion  that  is  green  and  bears  the 
sex-organs.  This  strange  subterranean  and  saprophytic 
prothallium  is  in  marked  contrast  with  the  prothallia  of 
ferns  in  its  habits  and 
appearance.* 

118.  Selaginella.- 
The  Selaginella  forms 
are  much  more  numer- 
ous than  the  Lyco- 
podium forms,  being 
especially  abundant 
in  the  tropics,  and  are 
often  called  the  little 
club-mosses  on  ac- 
count of  their  smaller 
size  and  more  delicate 
texture.  It  is  these 
forms  that  are  com- 
mon in  greenhouses 
as  decorative  plants. 
There  are  often  no 
strobili  very  distinct 
from  the  leafy  stem, 
the  solitary  sporangia 
occurring  in  the  axils 
of  the  upper  leaves 
(Fig.  195). 

The  most  important  fact  in  connection  with  Selaginella 
is  that  all  the  sporangia  in  a  strobilus  do  not  produce  the 

*  The  gametophytes  of  Lycopodium  are  so  rarely  found  that  it  is 
not  expected  that  they  will  be  seen  by  the  student. 


FIG.  195. — Branch  of  Selaginella  bearing  strobili. 


A  TEXT-BOOK  OF   BOTANY 


same  kind  of  spores.  For  example,  certain  sporangia  (usu- 
ally the  lower  ones)  may  each  contain  four  large  spores 
(Fig.  196,  C  and  D),  while  the  other  sporangia  contain 

very  numerous  and  very 
much  smaller  spores 
(Fig.  196,  A  and  B). 
There  may  be  no  differ- 
ence in  the  appearance 
of  the  sporangia.  A 
plant  that  produces  two 
kinds  of  spores,  differing 
in  size,  is  said  to  be  he- 
terosporous  (spores  dif- 
ferent). The  appear- 
ance of  this  condition 
is  a  very  important 
fact,  for  it  is  an  intro- 
duction to  the  appear- 
ance of  the  higher  plants. 
Difference  in  the  size 
of  spores  does  not  seem 
important;  but  when 
this  is  accompanied  by 
difference  in  the  gameto- 
phytes  produced,  it  is 
very  important.  When 
the  small  spore  germi- 
nates, it  produces  a  few- 
celled  gametophyte,  so  small  that  it  is  contained  entirely 
within  the  old  spore  wall.  This  gametophyte  produces 
one  antheridium,  and  this  antheridium  forms  the  bulk  of 
the  whole  body.  Therefore,  the  small  spore  produces  a 
very  small  male  gametophyte.  When  the  large  spore  ger- 
minates, it  produces  a  many-celled  gametophyte,  which 
bursts  through  the  spore  wall  and  becomes  partly  ex- 


FIG.  196. — Sporophylls  of  Selaginella:  A,  spo- 
rophyll  bearing  sporangium  that  produces 
numerous  small  spores  (B);  C,  sporophyll 
bearing  sporangium  that  produces  few 
large  spores  (Z)). 


HORSETAILS  AND  CLUB-MOSSES 


posed.  In  this  exposed  part  archegonia  appear,  and 
therefore  the  large  spore  produces  a  female  gametophyte 
(Fig.  197). 

In  Selaginella,  there- 
fore, the  two  kinds  of 
sex-organs  are  produced 
by  different  plants,  and 
we  speak  of  male  and 
female  gametophytes. 
The  connection  of  these 
two  kinds  of  gameto- 
phytes with  the  two 
kinds  of  spores  must  be 
kept  clear.  The  small 
spore  (microspore)  pro- 
duces the  male  gameto- 
phyte, and  the  large 
spore  (megaspore)  pro- 
duces the  female  ga- 
metophyte. It  must  be 
remembered,  also,  that 

with  this  change  the  gametophytes  have  become  much 
smaller  than  they  were  before,  and  are  no  longer  indepen- 
dent, in  the  sense  of  doing  chlorophyll  work. 

It  follows  that  in  the  life-history  of  Selaginella  there  is 
an  alternation  of  the  sporophyte  with  two  gametophytes. 
How  this  contrasts  with  the  life-history  of  an  ordinary  fern 
may  be  indicated  as  follows: 

Fern:  Gn£>o— S—  o— G~°>o— S— o— Gn£>o— S,  etc, 
Selaginella:  g~g> o— S~~g~~c~g> o— S~~g~~g~g> o,  etc. 

119.  Coal. — The  ferns,  equisetums,  and  lycopods  were 
associated  together  during  the  Coal-measures,  and  were 
the  most  conspicuous  plants  in  the  formation  of  coal.  The 
formation  of  peat,  already  referred  to  (§  101),  indicates  the 


FIG.  197. — Female  gametophyte  of  Selaginella, 
having  burst  through  the  wall  of  the  mega- 
spore  (m),  and  bearing  archegonia  (a)  and 
rhizoids  (r)  upon  its  exposed  part;  somewhat 
diagrammatic. 


206  A  TEXT-BOOK  OF  BOTANY 

first  stages  in  coal-formation.  During  the  Coal-measures 
there  were  very  extensive  areas  of  swampy  land  covered 
with  a  luxuriant  vegetation,  consisting  principally  of  ferns, 
equisetums,  and  lycopods.  The  dead  bodies  of  these 
plants  accumulated  in  immense  deposits  in  the  swamp 
waters;  and  when  a  sinking  of  the  land  brought  it  under 
water,  sediments  were  deposited  upon  the  accumulated 
vegetation  and  it  was  gradually  changed  into  coal.  Suc- 
cessive risings  and  sinkings  of  the  'land  surface  brought 
about  an  alternation  of  vegetation  and  sediments,  and  so 
the  coal  lies  in  beds  of  varying  thickness.  The  ferns, 
equisetums,  and  lycopods  are  often  spoken  of  as  peculiarly 
useless  plants;  but  when  one  considers  the  part  they 
played  in  coal-formation,  and  the  importance  of  coal  in  our 
civilization,  it  is  evident  that  no  plants  have  done  more  for 
human  welfare. 

The  different  kinds  of  coal  depend  upon  the  amount  and 
kind  of  changes  in  this  old  buried  vegetation.  For  example, 
hard  coal  (anthracite)  has  been  changed  most,  containing 
eighty-five  per  cent  or  more  of  carbon;  while  soft  (bitumi- 
nous) coal  contains  only  fifty  to  seventy-five  per  cent  of 
carbon.  It  will  be  remembered  that  green  plants  take 
carbon  dioxide  from  the  air  and  use  the  carbon  in  building 
their  bodies  (§  14).  Therefore,  the  enormous  amount  of 
carbon  contained  in  coal  deposits  was  in  the  main  drawn 
from  the  air  by  plants.  When  coal  is  burned  now  there 
is  made  a  tardy  return  of  carbon  dioxide  to  the  air  for  that 
which  was  taken  from  it  millions  of  years  ago. 

The  coal-fields  of  the  United  States  are  the  greatest  in 
the  world  that  are  now  being  worked;  but  the  coal-fields 
of  China  are  probably  even  greater.  The  coal  of  the  United 
States  is  all  soft  coal,  except  in  the  mountain  region  of 
Pennsylvania,  where  the  bituminous  coal  has  been  changed 
into  anthracite. 


CHAPTER  XII 

GYMNOSPERMS 

120.  Summary. — The    ferns,     equisetums,    and    lyco- 
pods  are  representatives  of  the  third  great  division  of  the 
plant  kingdom,  the  Pteridophytes  (fern  plants).    Their  con- 
tributions to  the  progress  of  plants  are  very  important  and 
may  be  summarized  as  follows: 

(1)  Leafy  sporophytes. — All   Pteridophytes  have  leafy 
sporophytes,  and  all  Bryophytes  have  leafless  ones,  so  that 
this  change  is  not  only  great,  but  also  complete.     The  leafy 
sporophyte  means  also  a  vascular  system  and  roots,  and 
therefore  these  structures  are  introduced  by  the  Pterido- 
phytes. 

(2)  Sporophylls. — The  setting  apart  of  certain  leaves  to 
bear  sporangia  makes  a  division  of  work  between  foliage 
leaves  and  sporophylls,  and  the  arrangement  of  the  sporo- 
phylls  into  the  distinct  cluster  known  as  the  strobilus  marks 
another  advance. 

(3)  Heterospory. — The  occasional  appearance  of  hetero- 
sporous  plants  among  Pteridophytes,  as  Selaginella  and  a 
few  other  forms,  is  noteworthy,  because  all  the  plants  of  the 
next   and    highest   group   are   heterosporous.     Associated 
with  heterospory  is  a  great  reduction  in  the  size  of  the  two 
gametophytes,  which  are  so  small  that  they  project  little  if 
at  all  from  the  spores  which  produce  them. 

121.  The  four  great  plant  groups. — Three  of  the  great 
divisions  of  the  plant  kingdom  have  been  considered.     The 

207 


208 


A  TEXT-BOOK  OF  BOTANY 


fourth  differs  from  them  all  in  producing  seeds,  and  hence 
is  called  Spermatophytes  or  seed-plants.  It  may  be  well 
to  give  certain  prominent  characters  that  will  serve  to  dis- 
tinguish these  four  primary  groups.  It  must  not  be  sup- 
posed that  these  are  the  only  characters,  or  even  the  most 
important  ones  in  every  case,  but  they  are  convenient  for 
our  purpose. 

(1)  Thallophytes. — Thallus.  body,  but  no  archegonia. 

(2)  Bryophytes. — Archegonia,  but  no  vascular  system. 

(3)  Pteridophytes. — Vascular  system,  but  no  seeds. 

(4)  Spermatophytes. — Seeds. 

It  will  be  noticed  that  for  each  of  the  first  three  groups 
two  characters  are  given,  one  a  positive  character  that 

belongs  to  it,  the 

•-•«5^,  ffilHHHI     other    a     negative 

character  that  dis- 
tinguishes it  from 
the  group  above, 
and  becomes  the 
positive  charac- 
ter of  that  group. 
For  example,  thal- 
lus  bodies  are 
found  among  Bryo- 
phytes, and  the  pro- 
thallium  of  a  Fern 
is  a  thallus  body; 
but  plants  whose 
thallus  bodies  do 
not  bear  arche- 
gonia are  Thallo- 
phytes. Also,  arch- 
egonia are  produced  by  Pteridophytes  as  well  as  by 
Bryophytes,  but  archegonium-bearing  plants  without  a 
vascular  system  can  be  only  Bryophytes.  Both  Pteri- 


FIG.  198. — A  cycad  with  columnar  stem. — After  STRAS- 
BURGER. 


210 


A  TEXT-BOOK  OF  BOTANY 


dophytes  and  Spermatophytes  have  vascular  systems,  but 
only  the  latter  produce  seeds. 

122.  General  characters  of  Gymnosperms. — The  Gymno- 
sperms  are  one  of  the  two  groups  of  seed-plants,  the  most 
familiar  ones  in  temperate  regions  being  pines,  spruces, 
hemlocks,  cedars,  etc.,  the  group  commonly  called  ever- 
greens. It  is  an  ancient  group,  for  its  representatives  were 
associated  with  the  giant  club-mosses  and  horsetails  in 
the  forest  vegetation  of  the  Coal-measures.  Only  about 
four  hundred  species  exist  to-day  as  a  remnant  of  its  former 
display,  although  it  still  forms  extensive  forests.  Gymno- 
sperms are  very  diverse  in  habit.  They  are  all  woody 
forms,  but  they  may  be  gigantic  trees,  trailing  or  straggling 
shrubs,  or  high-climbing  vines.  There  are  two  prominent 
living  groups  of  Gymnosperms. 


FIG.  200. — A  cycad  with  tuberous  or  short  thick  stem. 

Cycads  are  tropical  forms  with  large  fern-like  leaves. 
The  stem  is  either  a  columnar  shaft  crowned  with  a  rosette 


GYMNOSPERMS  211 

of  large  compound  leaves,  with  the  general  habit  of  tree- 
ferns  and  palms  (Figs.  198  and  199);  or  they  are  like  great 
tubers,  crowned  in  the  same  way  (Fig.  200).  The  tuberous 
stems  are  often  more  or  less  buried,  as  in  our  only  cycad 
from  the  United  States 
(Florida),  illustrated  in 
Fig.  200.  In  ancient 
times  cycads  were 
very  abundant,  but 
now  they  are  rep- 
resented by  about 
eighty  species  scat- 

fprpH    i hrnno-Vi    tViP    nri        FlG>  20L~ Two  view8  of  the  8perm  of  a 

showing  its  spiral  form  and  many  cilia. 

ental     and    occidental 

tropics.  They  are  especially  interesting  in  their  resem- 
blances to  ferns,  and  some  of  them  might  be  mistaken  for 
ferns  did  they  not  bear  large  seeds.  In  addition  to  their 
fern-like  leaves,  they  have  in  the  structure  of  the  stem 
many  fern  characters;  and  they  have  coiled  sperms  with 
many  cilia  (Fig.  201),  as  do  the  ferns.  They  are  very 
interesting  to  study;  but  it  is  easier  to  obtain  the  Gym- 
nosperm  characters  from  the  other  group,  whose  forms  are 
far  more  familiar  and  easily  obtained. 

Conifers  are  the  common  Gymnosperms,  often  forming 
great  forests  in  temperate  regions.  Some  of  the  forms  are 
widely  distributed,  as  the  pines;  while  some  are  now  very 
much  restricted,  as  the  gigantic  redwoods  (Sequoia)  of  the 
Pacific  slope.  The  habit  of  the  body  is  quite  characteristic, 
a  central  shaft  extending  to  the  very  top  (Fig.  42).  In 
many  cases,  the  branches  spread  horizontally,  with  dimin- 
ishing length  to  the  top,  forming  a  conical  outline,  as  in  the 
firs.  This  habit  gives  the  conifers  an  appearance  very 
distinct  from  that  of  the  other  trees. 

Another  peculiar  feature  is  the  needle-leaf.  These  leaves 
have  a  small  surface  and  very  heavy  protecting  cells,  being 


212  A   TEXT-BOOK  OF  BOTANY 

able  to  endure  the  cold  of  winter  (Figs.  30  and  31).  As 
there  is  no  regular  period  for  the  fall  of  leaves,  as  in  the 
deciduous  trees,  the  trees  are  always  clothed  with  them, 
and  hence  are  called  evergreens.  A  notable  exception  to 
the  evergreen  habit  of  conifers  is  that  of  the  common  larch 
or  tamarack,  which  sheds  its  leaves  every  season. 

The  great  body  of  the  plant  is  highly  organized  for  work, 
with  its  roots,  stem,  and  leaves,  and  an  elaborate  vascular 
system  connecting  them  all.  The  wood  of  the  conifers  is 
peculiar  in  its  very  regular  grain,  splitting  easily;  and  its 
generally  "soft"  character  is  quite  distinct  from  the  so- 
called  "hard  woods."  Throughout  the  body  there  are 
also  numerous  resin-ducts,  whose  contents  give  a  peculiar 
aroma  to  the  wood. 

123.  Strobili. — The  cones  borne  by  the  conifers  are 
well  known,  and  suggest  at  once  the  strobili  of  certain 
Pteridophytes.  There  are  two  kinds  of  strobili,  however, 
one  being  the  conspicuous  seed-bearing  cones  of  common 
observation,  the  other  much  smaller  and  much  less  per- 
sistent cones  (Fig.  202).  In  Selaginella  (§  118),  it  will  be 
remembered,  there  are  two  kinds  of  sporangia  in  a  single 
strobilus;  but  in  conifers  these  two  kinds  of  sporangia  are 
in  separate  strobili  or  cones.  In  describing  the  two  cones 
the  pine  may  be  used  as  an  illustration. 

The  small  cone  (Fig.  202,  d,  and  Fig.  203,  A)  is  made 
up  of  sporophylls  that  look  like  small  scales;  and  on  the 
lower  surface  of  each  scale  there  are  two  sporangia  (Fig. 
203,  B  and  C),  each  sporangium  containing  very  numerous 
small  spores  (microspores).  All  of  these  structures  received 
names  long  before  their  relations  to  the  lower  plants  were 
known;  but  as  these  names  are  well  known  it  is  convenient 
to  use  them.  The  small  spores  were  called  pollen  grains  or 
simply  pollen;  the  sporangia  containing  them  were  called 
pollen  sacs  ;  and  the  sporophyll  bearing  the  sporangia  was 
called  a  stamen.  The  strobilus  or  cone,  therefore,  is  a 


GYMNOSPERMS 


213 


group  of  stamens;  and  to  distinguish  it  from  the  other  cone 
it  may  be  called  the  staminate  cone.     It  should  be  remem- 


i a 


b— 3 


FIG.  202. — Tip  of  pine  branch,  showing  carpellate  cones  of  first  year    (a),  second 
year  (6),  and  third  year  (c);  also  a  cluster  of  staminate  cones  (rf). 

bered,  however,  that  all  these  structures  are  found  also 
among  Pteridophytes,  though  they  are  not  called  by  these 
names. 

The  large  cone  of  the  pine  is  made  up  of  sporophylls 


214: 


A  TEXT-BOOK  OF  BOTANY 


that  become  very  thick  and  hard  (Fig.  204,  A),  and  that 
are  packed  closely  together  until  they  spread  apart  to  let 
out  the  seeds  (Fig.  202,  c).  On  the  upper  side  of  each 
sporophyll,  near  its  base,  there  are  two  sporangia  (Fig.  204, 
B  and  C),  in  each  one  of  which  there  is  a  single  large  spore 
(megaspore).  So  large  is  the  spore  that  it  looks  like  a 


FIG.  203. — Staminate  cone  of  pine:  A ,  section  of  cone,  showing  sporophylls  (stamens) 
bearing  sporangia  (pollen  sacs);  B,  longitudinal  section  of  stamen,  through  one 
pollen  sac;  C,  cross-section  of  stamen,  showing  both  pollen  sacs;  D,  the  winged 
pollen  grain. — After  STRASBURGER. 

conspicuous  cavity  in  the  center  of  the  sporangium.  These 
structures  also  bear  old  names  that  may  be  used.  The 
sporangia  were  called  ovules  ;  and  the  sporophyll  bearing 
them  was  called  a  carpel.  The  large  spore  was  regarded 
only  as  a  cavity  in  the  ovule.  The  cone,  therefore,  is  a 
group  of  carpels;  and  to  distinguish  it  from  the  staminate 
cone  it  may  be  called  the  carpellate  cone. 


GYMN'OSPERMS 


215 


It  is  evident  that  the  pine-tree,  bearing  these  sporangia, 
is  the  sporophyte  in  the  life-history;  that  is,  it  is  the  sex- 
less generation.  The  sporophyte  has  now  become  so  prom- 


FIG.  204. — Carpellate  cone  of  pine:  A,  cone  partly  sectioned;  B,  young  carpel 
(sp.orophyll)  with  two  ovules  (sporangia)  ;  C,  old  carpel  with  mature  seeds. — 
After  BESSEY. 

inent  that  it  seems  to  be  the  whole  plant,  and  it  is  interest- 
ing to  know  what  has  become  of  the  gametophytes  with 
their  sex-organs. 

124.  Gametophytes. — As  the  pine  is  a  heterosporous 
plant,  there  are  male  and  female  gametophytes.  The  small 
spores  (pollen  grains)  germinate  and  produce  very  small 
male  gametophytes.  As  in  Selaginella  (§  118),  only  a  few 
cells  are  formed,  and  these  remain  in  the  pollen  grain  (Fig. 
15 


216 


A  TEXT-BOOK  OF  BOTANY 


203,  D).     Such  a  gametophyte  has  become  so  small  that 
it  can  be  seen  only  under  the  microscope.     Among  the 

cells  formed,  however, 
are  two  sperms.  These 
sperms  have  no  cilia,  and 
hence  it  is  evident  that 
they  do  not  reach  the  egg 
by  swimming. 

The  single  large  spore 
within  the  ovule  (spo- 
rangium) is  peculiar  in 
never  leaving  it;  that  is, 
it  is  never  shed,  as  are 
other  spores.  It  pro- 
duces a  many-celled  fe- 
malegametophyte,justas 
does  Selaginella  (§  118); 
and  on  this  gametophyte 
archegonia  are  formed 
(Fig.  205).  Since  the 
large  spore  is  not  shed, 
the  female  gametophyte 
it  produces  lies  embed- 
ded in  the  center  of  the 
ovule,  like  an  internal 
parasite  (Fig.  205,  g). 
It  is  evident  now  why  the  gametophytes  of  such  plants 
are  not  ordinarily  seen,  for  one  is  within  the  pollen  grain 
and  the  other  is  within  the  ovule. 

125.  Fertilization. — Before  fertilization  can  take  place, 
the  pollen  grain,  which  develops  the  male  gametophyte  with 
its  sperms,  must  be  brought  to  the  ovule,  which  contains 
the  female  gametophyte  with  its  archegonia.  The  pollen 
grains  (microspores)  are  formed  in  very  great  abundance, 
are  dry  and  powdery,  and  are  scattered  far  and  wide  by 


FIG.  205. — A,  section  showing  the  relative  po- 
sitions of  bract  (b),  scale  (s),  and  ovule  (o) 
in  a  pine  cone,  the  female  gametophyte  (g) 
being  very  young ;  B,  enlarged  section 
through  the  ovule  a  year  later,  showing  the 
female  gametophyte  (0)  bearing  two  arche- 
gonia (a)  which  are  being  reached  by  the 
penetrating  pollen  tubes  (t). 


GYMXOSPERMS  217 

the  wind.  In  the  pines  and  their  allies  the  pollen  grains 
are  winged  (Fig.  203,  Z>),  so  they  are  well  organized  for 
wind  distribution.  This  transfer  of  pollen  from  the  stami- 
nate  cone  to  the  carpellate  cone  is  called  pollination,  and 
the  agent  of  transfer  is  the  wind.  So  abundant  is  the  pol- 
len of  conifers  that  it  sometimes  falls  like  a  yellow  shower, 
and  the  occasionally  reported  "showers  of  sulphur"  are 
really  showers  of  pollen  from  some  forest  of  conifers.  Some 
pollen  must  reach  the  ovules,  and  to  insure  this  it  must  fall 
like  rain.  To  aid  in  catching  the  falling  pollen  the  scale- 
like  carpels  of  the  cone  spread  apart;  and  the  pollen  grains 
sliding  down  their  sloping  surfaces  collect  in  a  little  drift 
at  the  bottom  of  each  carpel,  where  the  ovules  are  found. 
In  this  position  each  of  the  most  favorably  placed  pollen 
grains  begins  to  put  forth  a  tube  (pollen  tube).  This  tube, 
containing  the  two  sperms  in  its  tip,  grows  through  the 
ovule,  and  reaches  the  archegonia  (Fig.  205,  t).  Then  the 
sperms  are  discharged,  and  when  they  reach  the  egg 
fusion  takes  place  and  fertilization  is  accomplished. 

126.  Embryo. — The  oospore  that  has  been  formed  within 
the  archegonium  at  once  germinates  and  begins  to  form  the 
young  plantiet  (embryo),  which  of  course  is  still  within  the 
ovule.     This  embryo  continues  to  grow,  feeding  upon  the 
female  gametophyte  that  surrounds  it.     It  is  evident  that 
this  embryo  is  the  young  sporophyte  of  the  next  generation. 

127.  Seed. — While  the  embryo  is  developing,  some  im- 
portant changes  are  taking  place  in  the  ovule  outside  of 
the  female  gametophyte.     The  most  notable  change  is  the 
formation  of  a  hard,  bony  covering,  which  hermetically 
seals  the  structures  within,  so  that  further  development  is 
checked.     In  this  way  the   ovule  (sporangium)  has  been 
transformed  into  what  is  called  a  seed,  the  distinguishing 
structure  of  seed-plants. 

If  a  pine  seed  is  cut  open,  the  embryo  (young  sporophyte) 
may  be  seen  embedded  in  the  center  (Fig.  206);  around 


218  A  TEXT-BOOK  OF  BOTANY 

it  is  packed  nutritive  tissue  (often  called  endosperm},  which 
is  the  female  gametophyte;  and  outside  of  that  there  is 
found  the  bony  seed-coat  (testa).  In 
this  condition  of  suspended  animation 
the  embryo  may  continue  for  a  long 
time,  certainly  until  the  next  season, 

PerhaPs  for  many  seasons-     When  the 
seed   comes   into    favorable    conditions 
and   "awakens,"    the    embryo    escapes 
male  gametophyte),      an(j    grows    into    the    pine-tree.      This 

which  is  invested  by  . 

the  hard  testa.  awakening  of  the  seed  is  usually  called 

its  "germination,"  but  it  must  not  be 
confused  with  the  germination  of  spores  and  oospores. 
The  "germination"  of  the  seed  is  merely  the  resumption 
of  growth  by  the  embryo  and  its  escape  from  the  seed. 
In  seed-plants,  therefore,  there  are  two  distinct  periods  in 
the  growth  of  the  sporophyte,  the  period  within  the  seed 
(when  it  is  called  an  embryo),  and  the  period  outside  of 
the  seed;  and  these  two  periods  may  be  separated  from 
one  another  by  a  long  period  of  time.  For  an  account  of 
seed  germination  see  Chapter  V. 

128.  Timber  from  Conifers. — The  conifers  are  the  most 
important  source  of  timber  in  the  United  States,  yielding 
at  least  three-fourths  of  our  supply.  They  are  usually 
called  "soft  woods"  in  distinction  from  the  so-called 
"hard  woods,"  such  as  oak;  but  there  are  soft  and  hard 
woods  in  both  groups.  The  United  States  is  notable  for  its 
variety  of  pines,  broadly  grouped  into  the  soft  white  pine 
and  the  hard  yellow  pines.  Our  principal  supplies  come 
from  the  white  pine  forests  about  the  Great  Lakes  and  the 
yellow  pine  forests  of  the  Southern  States;  but  the  forests 
of  the  former  region  have  been  cut  over  so  ruthlessly  for  so 
long  a  time  that  the  supply  of  white  pine  is  diminishing. 
A  few  years  ago  the  white  pine  furnished  nearly  one-third 
of  all  the  timber  produced  by  the  United  States.  It  is  very 


GYMNOSPERMS  219 

important  to  learn  how  to  obtain  white  pine  with  the  least 
possible  waste,  for  the  usual  methods  will  soon  destroy  all 
of  our  supply. 

The  pine  forests  of  the  South,  yielding  in  increasing 
amount  the  very  valuable  timber  of  the  hard  wood  yellow 
pines,  are  very  extensive.  Chief  among  these  yellow  pines 
is  the  Georgia  pine,  being  the  principal  species  over  an 
area  fifty  to  one  hundred  and  fifty  miles,  wide  and  extend- 
ing along  the  coast  region  from  North  Carolina  to  eastern 
Texas.  This  great  Southern  pine  region  is  producing  more 
and  more  timber  as  the  supply  from  the  Northern  white 
pine  is  diminishing. 

The  coniferous  forests  mentioned  above  belong  to  the 
general  Atlantic  region,  which  extends  from  the  Atlantic 
Coast  to  the  Mississippi  Valley;  but  there  is  a  Pacific  region 
extending  from  the  Rocky  Mountains  to  the  Pacific  Coast, 
all  of  whose  immense  forests  are  conifers.  These  Western 
forests  are  mainly  in  the  mountains,  and  have  been  most 
wastefully  treated  in  cutting  for  timber,  clearing,  and  per- 
mitting the  ravages  of  fire.  Two  famous  coniferous  trees  of 
California  are  the  redwood  and  the  big  tree.  The  former 
yields  a  very  valuable  lumber,  and  the  latter  is  the  largest 
American  tree.  The  big  trees  are  found  in  scattered  groves 
along  the  western  slopes  of  the  Sierra  Nevada,  a  number  of 
which  are  carefully  preserved.  The  height  of  the  standing 
trees  reaches  325  feet,  but  a  fallen  tree  is  estimated  to  have 
been  over  400  feet  high.  The  diameter  of  the  trunk  near 
the  ground  sometimes  reaches  30  to  35  feet. 

129.  Resin  and  turpentine. — The  conifers  in  general 
contain  resins,  and  from  certain  pines  the  common  resin 
(or  rosin)  and  turpentine  of  commerce  are  obtained.  Usu- 
ally incisions  are  made  into  the  wood  of  the  trees  and  a  resi- 
nous liquid  exudes,  which  is  crude  turpentine.  This  liquid 
is  distilled,  the  oil  or  spirit  of  turpentine  coming  off  and 
being  collected,  and  the  resin  remaining  behind  in  the  still. 


CHAPTER  XIII 

ANGIOSPERMS 

130.  General  characters. — This  is  the  greatest  group  of 
plants,  both  in  numbers  and  importance.     It  comprises 
more  than  100,000  species,  and  forms  the  most  conspicuous 
part  of  the  vegetation  of  the  earth.     It  includes  herbs, 
shrubs,  and  trees  in  profusion,  and  represents  the  plant 
kingdom  at  its  highest  development.     There  is  the  greatest 
possible  variety  in  habit,  size,  and  duration:  from  minute 
floating    forms    to    gigantic    trees;    erect,    prostrate,    and 
climbing;  aquatic,  terrestrial,  epiphytic;  from  a  few  days  to 
centuries  in  duration. 

The  most  striking  feature  of  the  Angiosperms  to  the 
ordinary  observer  is  that  the  majority  of  them  produce 
what  every  one  recognizes  as  flowers;  and  hence  they  are 
often  spoken  of  as  flowering  plants.  The  production  of 
flowers,  however,  is  not  the  real  distinction  of  the  group, 
but  it  is  a  very  prominent  feature  and  suggests  the  group  to 
most  people  better  than  any  other  character. 

The  general  structure  of  the  roots,  stems,  and  leaves  of 
this  great  group  was  presented  in  Chapters  II,  III,  and  IV, 
so  that  there  remain  for  consideration  the  flower  and  the 
structures  associated  with  it. 

131.  The    flower. — It    is    impossible    and    unnecessary 
to  define  a  flower,  but  it  is  not  at  all  difficult  to  recognize 
ordinary  flowers.     They  are  objects  of  such  common  ex- 
perience that  no  one  is  at  a  loss  to  understand  what  is 
meant  when  the  word  is  used.     The  parts  of  a  flower  may 

220 


ANGIOSPERMS 


221 


be  understood  best  by  selecting  for  description  some  simple 
flower  that  has  all  the  floral  members,  as,  for  example,  the 
buttercup. 

In  such  a  flower  there  are  four  distinct  sets  of  members 
(Fig.  207).  The  outermost  set  has  the  color  and  the  form 
of  small  leaves,  each 
member  being  called 
a  sepal,  and  the  whole 
set  the  calyx.  The 
next  inner  set  is  usu- 
ally the  showy  one, 
with  members  of  rel- 
atively large  size, 
delicate  texture,  and 
bright  color,  each 
member  being  called 
a  petal,  and  the  whole 
set  the  corolla.  The 
set  just  within  the  co- 
rolla comprises  the  stamens,  which  produce  the  pollen. 
The  central  set  is  made  up  of  the  carpels,  which  contain 
the  ovules  that  are  to  become  seeds. 

The  endless  variations  of  these  sepals,  petals,  stamens, 
and  carpels,  make  the  differences  among  flowers,  and  it  is 
astonishing  in  how  many  ways  the  variations  of  four  parts 
can  be  combined.  It  will  be  impossible  to  describe  even 
the  conspicuous  variations  and  combinations,  but  certain 
general  tendencies  may  be  pointed  out.  It  is  important 
for  the  student  to  examine  as  many  of  the  common  flowers 
of  his  neighborhood  as  possible,  and  to  discover  how  they 
differ  from  one  another;  for  it  is  these  floral  differences 
that  are  most  used  in  classifying  Angiosperms. 

132.  Sepals. — While  the  sepals  generally  look  like  small 
green  leaves,  this  is  by  no  means  always  true.  Sometimes 
they  are  as  brightly  colored  as  petals;  and  often  they  appear 


FIG.  207. — Flower  of  peony  :  k,  sepals;  c,  petals; 
a,  stamens;  g,  carpels. — After  STRASBURGER. 


222 


A  TEXT-BOOK  OF  BOTANY 


united,  so  that  the  calyx  is  a  little  cup  or  tube  (Fig.  208). 
In  any  case,  the  calyx  is  useful  in  the  bud  condition  of  the 
flower  in  protecting  the  more  delicate  parts  within.  Some- 
times the  sepals  and  the  petals  look  so  much  alike  that  they 
are  spoken  of  together  as  the  perianth,  as  in  the  common 
lily  (Fig.  274).  Occasionally  there  is  only  one  floral  set 
outside  the  stamens;  and  it  has  become  the  custom  to  call 
it  a  calyx,  assuming  that  the  corolla  is  lacking.  In  still 
other  cases,  there  are  no  floral  members  outside  the  sta- 
mens; and  then  the  flower  is  said  to  be  naked. 

133.  Petals. — The    attractiveness    of    flowers    usually 
depends  upon  their  petals,  and  hence  their  differences  in 


A  B  C 

FIG.  208. — Flower  of  tobacco:  A.,  sympetalous  corolla,  calyx  urn-like;  B,  tube  of 
corolla  cut  open  and  showing  attachment  of  stamens;  C,  the  pistil,  showing 
ovary,  style,  and  stigma. — After  STRASBURGER. 

color  and  form  are  things  of  common  experience.  In  many 
flowers  the  petals  are  entirely  distinct  from  one  another 
and  can  be  pulled  off  separately.  In  many  other  flowers, 


ANGIOSPERMS  223 

however,  the  petals  appear  to  be  united  so  that  the  corolla 
becomes  a  cup,  urn,  tube,  funnel,  or  the  like  (Figs.  208 
and  209).  This  condition  of  the  corolla  is  so  constant  in 
the  highest  group  of  Angiosperms  that  the  group  is  called 
the  Sympetalce,  because  the  corollas  are  sympetalous  (petals 
together). 

In  many  flowers  with  sympetalous  corollas  there  is  an 
irregular  development,  so  that   the   mouth   of  the   tube, 


FIG.  209. — Sympetalous  flowers:  A,  bluebell;  B,  phlox;  C,  dead-nettle;  D,  snap- 
dragon; E,  toadflax. — After  GRAY. 

instead  of  being  regular,  is  divided  into  two  unequal  lips, 
as  in  the  mints  and  many  others  (Fig.  209,  C — E).  Such 
flowers  are  said  to  be  bilabiate  (two-lipped),  and  on  this 
account  the  Mint  Family  is  named  Labiatce.  Such  corollas 
may  have  further  irregularities  in  the  form  of  more  or 
less  conspicuous  projections  at  the  base  called  spurs  (Fig. 
209,  E).  It  must  not  be  supposed  that  irregular  growths 
are  found  only  in  connection  with  sympetalous  corollas; 
for  the  sweet  pea  represents  a  great  family  in  which  the 
petals  are  all  separate,  and  yet  they  are  very  much  unlike; 
and  in  the  violet,  whose  petals  are  distinct,  one  of  them 
has  a  conspicuous  spur. 

The  corolla  is  useful  in  protecting  the  young  stamens 
and  carpels,  but  it  is  alsc  associated  with  the  visits  of 
insects,  a  subject  which  will  be  spoken  of  later. 


A  TEXT-BOOK   OF  BOTANY 


134.  Stamens. — From  our  study  of  Gymnosperms  (§  123), 
the  stamen  of  the  Angiosperm  flower  is  recognized  as  a  spo- 
rophyll  bearing  sporangia,  which  pro- 
duce the  small  spores  (microspores) 
called  pollen  grains.  The  stamen  of 
Angiosperms,  however,  has  two  very 
distinct  regions.  There  is  a  stalk, 
which  is  usually  slender  and  long, 
called  the  -filament;  and  at  the  top  of 
this  there  is  the  knob-like  sporan- 
gium-bearing region  called  the  anther 
(Fig.  210). 

A   cross-section    of   a   very  young 
FIG.  210.— Front  (A)  and    anther  usually  shows  that  it  contains 
back  (£)  views  of  a  sta-    four  sporangia,  that  is,  four  regions  in 

men,  showing  filament  mi\ 

(/)  and  anther  (P),  the    which   spores   are   formed  (Fig.   211). 
latter  including  two  poi-    Ag  th     anther  matures,   the   two   re- 

len  sacs. — After  SCHIM- 

PER.  gions  on   each  side   run   together,  so 


Fio.  211. — Cross-section  of  a  very  young  anther  of  a  lily,   showing  the  four  de- 
veloping sporangia. 


ANGIOSPERMS 


225 


that  the  anther  comes  to  contain   only  two   spore  cham- 
bers (Fig.  212).     These   two  spore  chambers  are  plainly 


FIG.  212 — Cross-section  of  a  mature  anther  of  a  lily,  much  larger  than  that  shown 
in  Fig.  211,  showing  the  two  chambers  formed  by  the  four  sporangia,  and  also 
the  region  of  opening  («). 


FIG.  213. — Anthers    opening   by    terminal    pores:     A,   Solanum;    B,   Arbutus;   C 
Vaccinium. — A  and  B,  after  ENGLER  and  PRANTL;  C,  after  KERNER 


A  TEXT-BOOK  OF  BOTANY 


FIG.  214. — Section  of  the  flower  of  an 
Althaea,  showing  sepals  (a),  petals 


visible  from  the  outside,  looking  like  two  sacs,  called  pol- 
len sacs.  Ordinarily,  therefore,  the  Angiosperm  stamen 
is  said  to  have  two  pollen  sacs. 

In  most  cases  the  pollen  sacs  must  open  so  that  the 
pollen  may  escape,  and  the  method  of  opening  differs  in 

different  flowers.  By  far  the 
most  common  way  is  for  each 
pollen  sac  to  split  open  length- 
wise, and  this  line  of  splitting 
is  usually  plainly  seen  on  the 
surface  of  the  unopened  sac 
(Fig.  210,  A).  In  some  cases, 
however,  each  pollen  sac  opens 
at  the  top,  either  by  a  short 
slit  or  by  a  pore-like  opening 
(Fig.  213,  A  and  B);  and  in 
some  cases,  as  among  the 

(6),  tube  of  stamens  (c)  enclosing     heaths,     this      pore-like     Open- 
style   (rf),  and  ovules    (e). — After      .  ,     t     • 

BERG  and  SCHMIDT.  ing  may  be  extended  into  a 

more  or  less  prominent  tube 

(Fig.  213,  C).  There  are  still  other  special  methods  of 
opening  pollen  sacs,  but  they  are  comparatively  rare. 

In  sympetalous  corollas  it  is  most  common  for  the 
stamens  to  appear  fastened  to  the  tube  of  the  corolla  (Fig. 
208,  B),  and  this  condition  is  usually  described  as  "stamens 
inserted  on  the  tube  of  the  corolla."  Stamens  may  also 
appear  united,  forming  a  tube,  as  in  mallows  (hollyhock, 
etc.)  (Fig.  214);  or  they  may  be  in  two  sets,  as  in  the  sweet 
pea,  in  which  nine  of  the  stamens  appear  united  and  the 
tenth  one  is  free  (Figs.  241  and  283). 

135.  Carpels. — It  has  been  noted  that  carpels  are  the 
sporophylls  that  be'ar  the  peculiar  sporangia  called  ovules 
(§  123).  There  is  a  striking  difference,  however,  between 
the  carpels  of  Gymnosperms  and  Angiosperms,  a  difference 
that  gives  names  to  the  two  groups.  In  Gymnosperms  the 


ANGIOSPERMS 


227 


ovules  are  exposed  on  the  surface  of  the  carpel,  while  in 
the  Angiosperms  they  are  enclosed  by  the  carpel  as  in  a 
closed  vessel.  Gymnosperm  means  "seed  naked/'  and 
Angiosperm  means  "seed  in  a  vessel ";  hence  the  names  of 
the  groups  refer  to  this  difference  in  the  carpels. 

The  carpel  of  an  Angiosperm  flower  has  the  general 
shape  of  a  flask  (Figs.  207  and  215,  A).  The  bulbous 
bottom  in  which  the  ovules  are  enclosed  is  called  the  ovary; 
the  neck  of  the  flask,  which  may  be  short  or  long,  is  called 
the  style;  and  upon  the  style,  either  on  its  top,  which  is 
often  knob-like,  or  along  its  side,  there  is  a  specially  pre- 
pared surface  to  receive  the  pollen,  known  as  the  stigma. 
This  stigmatic  surface,  when  ready  to  receive  the  pollen, 
is  sticky;  the  style,  unlike  the  neck  of  a  flask,  is  usually 
solid;  so  that  the  ovary  is  the  only  part  of  the  carpel  that  is 
hollow.  The  ovules  in  an  ovary  vary  in  number  from  a 
single  one  to  a  great 
number,  and  they  are 
borne  in  a  variety  of 
positions  on  the  inner 
wall  of  the  ovary. 

In  many  flowers 
the  carpels  remain 
separate  (Figs.  207 
and  215,  A),  as  in 
the  buttercups ;  but 
it  is  very  common  for 
all  the  carpels  of  a 
flower  to  unite  in  the 
formation  of  a  single 
structure,  whose  general  outline  is  that  of  a  single  car- 
pel. That  is,  it  has  a  single  ovary  and  may  have  a  single 
style  (Figs.  208,  C,  and  215,  C).  It  is  convenient  to  have  a 
word  to  apply  to  this  ovule-containing  structure,  whether 
it  consists  of  one  carpel  or  of  several  organized  together, 


FIG.  215. — A,  simple  pistils  (each  one  a  single 
carpel);  B  and  C,  compound  pistils  (each  one 
composed  of  several  carpels). — After  BERG 
and  SCHMIDT. 


A  TEXT-BOOK  OP  BOTANY 

and  such  a  word  is  pistil.  A  pistil,  therefore,  is  any  organ- 
ization of  carpels  that  appears  as  a  single  organ  with  one 
ovary.  A  pistil  composed  of  one  carpel  is  called  a  simple 
pistil  (Figs.  207  and  215,  A),  and  one  composed  of  more 
than  one  carpel  is  a  compound  pistil  (Figs.  208,  C,  and  215, 
C).  When  a  flower  has  one  pistil,  it  is  necessary  to  dis- 
cover whether  it  is  a  simple  or  a  compound  pistil,  and  if  it 
is  the  latter  to  determine  the  number  of  carpels  that  enter 
into  its  structure.  Sometimes  the  styles  are  separate 
(Fig.  215,  B],  or  the  single  style  is  cleft  more  or  less  deeply; 
and  in  either  case  the  answers  to  both  questions  are  very 
apparent.  But  often  the  style  is  single  throughout  and 
does  not  indicate  the  number  of  carpels.  In  that  case  the 
ovary  must  be  cross-sectioned,  and  if  the  section  reveals 
more  than  one  ovule  chamber  the  compound  character 
and  the  number  of  carpels  are  usually  apparent  (Fig.  216, 
B).  Sometimes,  however,  a  compound  ovary  may  have 
only  one  ovule  chamber,  and  in  this  case  the  number  of 


A  B 

FIG.  216. — Diagrammatic  cross-section  of  compound  ovaries:  A,  a  one-charnbered 
ovule  composed  of  three  carpels;  B,  a  three-chambered  ovule. — After  SCHIMPER. 

carpels  may  be  indicated  by  the  number  of  rows  of  ovules 
on  the  wall  (Fig.  216,  A}. 

It  is  necessary  to  know  something  about  the  structure 
of  the  Angiosperm  ovule  (Fig.  217).  That  it  is  a  sporangium 
containing  one  large  spore  (megaspore)  that  is  never  shed, 
was  pointed  out  in  connection  with  the  Gymnosperms 


ANGIOSPERMS 


229 


(§  123).  On  the  outside  of  this  ovule  one  or  two  special 
coverings  are  developed,  called  integuments.  These  integu- 
ments grow  up  about  the  ovule,  but  do  not  completely 
cover  it  at  the  top,  leaving  a  little  opening  called  the 
micropyle  (little  gate).  This  micropyle  is  a  very  important 


B 


Fio.  217. — Diagrammatic  longitudinal  sections  of  ovules,  showing  outer  (01)  and 
inner  (it)  integuments,  micropyle  (m),  nucellus  (n),  and  megaspore  (em),  the 
last  often  called  embryo  sac:  A,  erect  ovule;  B,  curved  ovule;  C,  inverted  ovule. 

feature  in  the  ovule  and  also  later  in  the  seed.  The  body 
of  the  ovule  within  the  integuments  is  called  the  nucellus, 
and  within  the  nucellus  the  large  spore  (megaspore)  lies 
embedded  (Fig.  217).  The  three  types  of  ovule  are  shown 
in  Fig.  217:  the  erect  ovule  (A),  the  curved  ovule  (B),  and 
the  inverted  ovule  ((7),  the  last  being  the  most  common. 

136.  Floral  numbers. — In  many  flowers  there  is  no 
regularity  in  the  number  of  members  in  each  set.  For 
example,  in  the  water-lily  petals  and  stamens  occur  in 
indefinite  numbers;  and  in  the  buttercup  the  same  is  true  of 
stamens  and  carpels.  In  most  flowers,  however,  definite 
numbers  appear  either  in  some  of  the  sets  or  in  all  of  them. 
When  these  definite  numbers  are  present,  they  are  prevail- 
ingly either  three  or  five;  that  is,  there  are  either  three  or  five 
sepals,  petals,  stamens,  and  carpels;  although  it  is  very 
common  to  have  two  sets  of  stamens,  in  which  case  they 
number  six  or  ten.  These  numbers  appear  so  constantly 
in  great  groups  that  the  two  grand  divisions  of  Angio- 


230 


A  TEXT-BOOK  OF  BOTANY 


sperms,  called  Monocotyledons  and  Dicotyledons,  are  char- 
acterized by  them,  the  former  having  the  parts  of  the 
flower  in  threes,  the  latter  in  fives.  This  does  not  mean 
that  all  flowers  of  these  two  divisions  have  one  or  the  other 
number,  but  that  these  are  the  prevailing  numbers  in  case 
there  is  a  definite  number  at  all.  Not  a  few  Dicotyledons 
have  flowers  with  the  parts  in  threes,  and  a  still  larger 
number  have  them  in  fours. 

137.  Staminate  and  pistillate  flowers. — In  many  cases 
stamens  and  pistils  are  not  found  together  in  the  same 
flower.  In  such  cases  there  are  staminate  flowers,  that  is, 
those  without  pistils;  and  pistillate  flowers,  that  is,  those 
without  stamens.  These  two  kinds  of  flowers  may  be 
borne  upon  the  same  plant,  which  is  then  said  to  be 
monoecious  (one  household);  or  upon  different  plants, 
which  are  then  said  to  be  dioecious  (two  households).  These 
terms  are  applied  indifferently  to  the  plants  or  to  the 
flowers,  either  the  plants  or  the  flowers  being  spoken  of  as 
monoecious  or  dioecious.  In  a  dioecious  plant,  therefore, 


FIG.  218. — Hypogynous  flower  of  Potentilla  (A),  and  epigynous  flower  of  apple 
(B). — After  ENGLEB  and  PRANTL. 

one  can  speak  of  staminate  and  pistillate  plants,  one  bear- 
ing fruit  and  seed  and  the  other  not.  Many  of  our  common 
trees,  as  willows  and  poplars,  are  dioecious;  and  many  more, 
as  oaks,  walnuts,  and  hickories,  are  monoecious. 


ANGIOSPERMS 


231 


138.  Hypogynous    and    epigynous    flowers. — In    many 
flowers   the  sepals,   petals,   and  stamens  are  seen  to  be 


FIG.  219. — Dogtooth  violet,  with  hypogynous  flowers  (Lily  Family). 


attached  under  the  ovary,  that  is,  the  ovary  appears  within 

the  flower   (Fig.   218,  A).     Such  a  flower  is  said  to  be 
16 


232 


A  TEXT-BOOK  OF  BOTANY 


hypogynous  (under  the  pistil)  ,  and  in  descriptions  of  flowers 
this  condition  is  often  called  "ovary  superior."  In  many 
other  flowers,  on  the  other  hand,  the  sepals,  petals,  and 
stamens  all  seem  to  be  attached  to  the 
top  of  the  ovary;  that  is,  the  o^ary  ap- 
pears beneath  the  flower  (Fig.  218,  B). 
Such  a  flower  is  called  epigynous  (upon 
the  pistil),  or  described  often  as  "ovary 
inferior."  This  is  a  very  important  dis- 
tinction, because  it  characterizes  great 
groups  of  plants;  for  example,  all  mem- 
bers of  the  Lily  Family  are  hypogynous 
(Fig.  219),  and  all  members  of  the  Ama- 
ryllis and  Iris  Families  are  epigynous 
(Fig.  220).  It  is  also  interesting  to  note 
that  all  the  plants  of  highest  rank  in 
their  respective  lines  have  epigynous 
flowers. 

139.  Flower  clusters.  —  In  many  cases 
a  single  flower  terminates  the  stem,  or 
flowers  may  occur  in   the  axils  of  ordi- 
But  more  frequently  flow- 

.         ,     _     .A  ,  f  , 

ers  occur  in  definite  clusters,  which  are 
characteristic    and    help    to    distinguish 
plants.     It  is  unnecessary  to  enumerate  all  the  forms  of 
flower  clusters  and   their   names,  but   some   of   the   more 
important  may  be  noted. 

One  of  the  most  common  kinds  of  clusters  is  that  in 
which  the  flowers  arise  along  an  axis,  resulting  in  a  more 
or  less  elongated  and  often  drooping  cluster.  This  is 
called  a  raceme,  and  the  flowers  may  be  loosely  or  densely 
arranged  (Fig.  221).  If  in  such  a  cluster  the  flowers  have 
no  stalks,  and  rest  directly  on  the  axis,  the  cluster  is  called 
a  spike,  as  in  the  common  plantain  (Fig.  222).  If  the 
cluster  is  flat-topped,  with  the  flower-stalks  rising  and 


ers  (Amaryllis  Fami-    nary  leaves. 

ly).  —  After   STRAS-  J 

BURGER. 


ANGIOSPERMS 


233 


spreading  like  the  braces  of  an  umbrella,  it  is  an  umbel,  as 
in  cherry  (Fig.  223),  wild  parsnip,  carrot,  etc.  (Fig.  224). 


If  one  can  imagine  the  flowers  of  an  umbel  without  any 
stalks,  so  that  they  would  be  packed  closely  together  at  the 


234: 


A  TEXT-BOOK  OF  BOTANY 


top  of  the  main  axis,  the  cluster  is  called  a  head,  the  most 
notable  illustrations  being  such  plants  as  the  sunflower  or 

dandelion,   whose  so-called 

r^-^       "  flowers  "  are  compact  clus- 
j  ters  or  heads  of  numerous 

small  flowers  (Figs.  298  and 
299). 


FIG.  223. — Umbel  of  cherry. — 
After  DUCHARTRE. 


FIG.  224. — Umbel  of  hemlock. 
After  SCHIMPER. 


ANGIOSPpRMS 


235 


140.  The  gametophytes. — The  gametophytes  of  Angio- 
sperms  are  even  more  reduced  than  those  of  Gymnosperms 
(§  124).  In  order  to  see  them,  special  preparations  for  the 
microscope  are  necessary,  but  with  the  help  of  illustrations 
some  idea  of  them  may  be  obtained.  By  the  pollen  grain 
(microspore)  three  cells  are  formed,  and  two  of  them  are 
male  cells  or  sperms;  these  three  cells  represent  the  male 
gametophyte  (Fig.  225). 
Within  the  large  spore 
(megaspore) ,  which  is 
retained  in  the  ovule, 
seven  cells  usually  ap- 
pear; and  one  of  these 
is  an  egg,  no  archego- 


FIG.  225. — Pollen  grain  containing 
a  three -celled  male  gameto- 
phyte; one  cell  represented  by 
its  nucleus,  the  two  other  cells 
being  male  cells. 


FIG.  226. — The  female  gametophyte  of  a  lily 
before  fertilization,  within  the  old  mega- 
spore  wall  eight  cells  or  their  nuclei  appear- 
ing, one  of  which  is  an  egg  (e) ;  the  pollen 
tube  enters  through  the  micropyle  (m). 


nium  to  contain  it  being  formed.  These  seven  cells  repre- 
sent the  female  gametophyte  before  fertilization  (Fig.  226). 
The  sperms  produced  by  the  pollen  must  reach  the  egg 
within  the  ovule.  The  stamens  chat  produce  the  pollen 
may  be  in  the  same  flower  as  the  pistil  that  contains  the 
ovules  with  their  eggs,  or  they  may  be  in  another  flower 
on  the  same  plant,  or  they  may  be  borne  by  an  entirely 
different  plant.  In  any  event,  the  first  thing  done  is  to 
transfer  the  pollen  to  the  pistil.  This  transfer,  that  is, 


236 


A  TEXT-BOOK  OF  BOTANY 


pollination  (§   125),  is  effected  in  many  Angiosperms  by 

insects,  and  how  this  is  brought  about  will  be  described 

later. 

The  pollen  grains  that  reach  the  stigma,  the  specially 

prepared  surface  for  receiving  them,  begin  to  put  out  pollen 
tubes.  These  tubes  grow  through  the 
stigma  and  enter  the  style;  grow  down 
the  style  and  enter  the  cavity  of  the 
ovary;  reach  the  ovules  and  enter  their 
micropyles;  and  finally  penetrate  the 
ovule  to  the  egg  (Fig.  227).  Through- 
out this  progress  of  the  tube  the  male 
cells  are  in  its  tip,  and  when  the  egg 
is  reached  they  are  discharged  from 
the  tube  and  one  of  them  fuses  with 
the  egg.  This  is  the  act  of  fertiliza- 
tion, and  through  it  the  egg  becomes 
an  oospore. 

An  important  difference  between 
Gymnosperms  and  Angiosperms  should 
be  noted  here.  In  Gymnosperms  the 
pollen  reaches  the  ovules,  for  they  are 
exposed;  but  in  Angiosperms  the  pol- 
len reaches  only  the  surface  (stigma) 

FIG.    227.-Diagrammatic     °f  the   Plstil  that  encloses  the  OVUleS. 

representation  of  pollen          141.  Embryo. — The  oospore,  lying 

tubes     penetrating    the  ,  .  ,  »      ,  ,  , 

style;  one  of  them  en-    in  the  midst  of  the  ovule,  at  once  be- 
tering  the  ovary  cavity,    ~ms  to  nrerminate,  and  forms  a  young 

passing   down    its  wall,     °  . 

and  reaching  the  female    plant   or  embryo.     While   the   embryo 


is  forming,  the  ovule  develops  a  hard 
coat  outside,  and  a  seed  is  the  result 
(Fig.  228).      The  general  structure  of  the  seed  and  how  the 
young  plant  escapes  from  the  seed  have  been  described  in 
Chapter  V. 

The   two  great  divisions  of   Angiosperms   are   named 


ANGIOSPERMS 


237 


FIG.  228. — Seed  of  violet,  one  figure  show- 
ing the  hard  testa,  the  other  the  em- 
bryo (young  sporophyte)  that  has 
developed  from  the  oospore. — After 
BAILLON. 


from  the  peculiar  character  of  their  embryos.  In  one 
division  the  root  is  developed  at  one  end  of  the  embryo 
and  the  single  cotyledon  at 
the  other  end,  the  stem 
coming  out  on  one  side.  In 
the  other  division  the  root 
is  developed  at  one  end  of 
the  embryo  and  the  stem  at 
the  other  end,  two  cotyle- 
dons coming  out  on  oppo- 
site sides  just  behind  the 
stem  tip.  Therefore,  the 
first  division  is  called  Mono- 
cotyledons (one  cotyledon), 
and  the  second  is  called  Di- 
cotyledons (two  cotyledons).  There  are  many  other  differ- 
ences between  Monocotyledons  and  Dicotyledons,  but  this 
difference  between  the  embryos  has  been  selected  to  form 
the  names. 

The  embryos  of  Angiosperms  differ  much  as  to  the  com- 
pleteness of  their  development  within  the  seed.  In  some 
plants  the  embryo  is  merely  a  mass  of  cells,  without  any 
organization  of  root,  stem,  or  leaf.  In  many  plants,  on 
the  other  hand,  the  embryo  becomes  highly  developed, 
showing  all  the  principal  organs  and  the  plumule  con- 
taining several  well-organized  young  leaves  (Chapter  V). 

142.  Seed. — The  seed  is  evidently  an  ovule  (sporangium) 
containing  a  female  gametophyte  which  has  developed  a 
new  sporophyte  (embryo).  This  complex  structure  is 
invested  by  the  hard  seed-coat,  and  is  a  protected  resting 
condition  of  the  plant. 

The  seed-coat  (testa)  in  Angiosperms  is  exceedingly 
variable  in  structure  and  appearance.  Sometimes  it  is 
smooth  and  glistening,  sometimes  pitted,  sometimes  rough 
with  warts  or  ridges.  In  many  cases  prominent  append- 


238 


A  TEXT-BOOK  OF  BOTANY 


ages  are  produced,  as  wings,  tufts  of  hairs,  etc.,  which  assist 
in  seed  dispersal,  a  subject  which  will  be  considered  later. 
143.  Fruit. — Accompanying  the  changes  in  ovules  in- 
volved in  the  formation  of  seeds,  there  are  other  changes 
in  the  surrounding  parts  resulting  in  the  formation  of  a 
fruit.  These  changes  may  involve  only  the  ovary  wall,  or 
they  may  include  also  other  adjacent  structures;  but  the 
whole  resulting  structure,  whatever  it  may  include,  is  called 
a  fruit.  The  fruits  of  Angiosperms  are  so  exceedingly 
diverse  that  it  will  be  possible  to  give  only  a  very  general 
outline  of  the  various  kinds. 

For  convenience,  those  fruits  will  be  considered  first 
that  represent  only  the  enlarged  and  modified  ovary. 
Such  fruits  may  be  placed  in  two  groups:  those  that  ripen 
dry  and  those  that  ripen  fleshy. 

(1)  DRY  FRUITS. — In  these  the  ovary  wall  not  only 
changes,  but  also  usually  becomes  hard  or  parchment-like. 
Dry  fruits  may  open  to  discharge  their 
seeds,  but  often  when  there  is  only  one 
seed  in  an  ovary  the  fruit  does  not  open. 
Thus  there  are  two 
groups  of  dry  fruits: 
the  dehiscent  (open- 
ing) and  the  indehis- 
cent  (unopening). 

a.  Dehiscent  fruits. 
— Dry  fruits  that  open 
are  in  general  called 
pods,  and  usually  they 
open  by  splitting,  as 
the  pods  of  peas  and 
beans.  The  great  fam- 
ily to  which  peas  and 
FIG.  229.-Pod  of  sweet  beans  belong  is  named  FlG-  230.— Capsule  of 

nea    dehismncr. —  Af-  iris  dphisrincr. — After 


pea   dehiscing, 
ter  GRAY. 


for     its     pod,     being 


iris  dehiscing.- 
GRAY. 


ANGIOSPERMS 


called  the  Leguminosce,  a  legume  being  a  special  kind  of 
pod  (Fig.  229).  When  a  pod  is  derived  from  a  compound 
pistil,  forming  a  fruit  of  several  cham- 
bers, it  is  more  commonly  called  a  cap- 
sule; and  capsules  differ  from  one  an- 
other in  the  way  the  chambers  are 
opened  (Fig.  230). 

b.  Indehiscent  fruits. — The  most  com- 
mon form  of  dry  fruits  that  do  not  open 
is  that  in  which  the  modified  ovary  wall 
invests  the  solitary  seed  so  closely  that 
the  fruit  looks  like  a  seed,  and  is  com- 
monly called  a  seed.  The  grain  of  cere- 
als is  such  a  seed-like  fruit,  as  is  also  the 
akene  of  sun-flowers,  dandelions,  etc. 
(Fig.  231). 

(2)  FLESHY  FRUITS. — In   some    cases 
the  whole  ovary  becomes  a  thin-skinned 
pulpy  mass  in  which  the  seeds  are  em- 
bedded, as  the  grape,  currant,  gooseberry,  tomato,  etc., 
such  a  fruit  being  a  berry.  .  Modifications  of  the  berry  are 
seen  in  such  fruits    as    the    orange 
and  the   lemon,  in    which  the  skin 
is  leathery;    and   in   such  fruits   as 
melons    and    pumpkins,    which    be- 
come   covered    with    a    hard    rind. 
Very  distinct    from    these    are    the 
stone-fruits  (drupes),  as  peach,  plum, 
cherry,  etc.,  in  which  the  ovary  wall 
ripens  in  two   layers,  the  inner  one 
being  very  hard,  forming  the  "stone/7 
and  the  outer  one  being  pulpy  (Fig. 
232).     In  general,  fleshy  fruits  do  not 

open;  but  the  banana  is  a   peculiar  fleshy  fruit  that  de- 
hisces. 


Fro.  231.  — Akene  of 
dandelion,  which  ta- 
pers above  into  a 
long  beak  bearing  a 
tuft  of  hairs. — After 
GRAY. 


Fro.  232. — Section  of  peach, 
showing  pulp  and  stone 
formed  from  ovary  wall 
and  enclosing  the  seed 
(kernel).— After  GRAY. 


240 


A  TEXT-BOOK  OF  BOTANY 


All  of  the  fruits  mentioned  above  include  only  a  modi- 
fied ovary  wall  with  its  contents,  but  many  of  the  most 


FIG.  233. — Raspberry:  A.  flower-stalk,  with  calyx, 
old  stamens,  and  prominent  receptacle,  from 
which  the  berry  (a  cluster  of  small  stone-fruits) 
has  been  removed  (J5). — After  BAILEY. 


FIG.  234. — Strawberry:  an 
enlarged  pulpy  receptacle 
in  which  numerous  small 
akenes  are  embedded. 


common  fruits  do  not  answer  to  this  description.     A  few 

of  the  most  conspicuous  of  these  will  serve  as  illustrations. 

A  number  of  the  best-known  fruits  have  been  named 

"berries"  that  are  not  berries  as  described  above.     For 


r 


FIG.  235. — Longitudinal  and  transverse  sections  of  apple,  showing  the  five-celled 
ovary  (core)  embedded  in  the  fleshy  cup  of  the  flower. 

example,  a  raspberry  is  a  mass  of  very  small  stone-fruits 
that  slips  from  the  enlarged  top  of  the  flower  axis  (recep- 


ANGIOSPERMS 


241 


tacle)  like  a  cap  (Fig.  233).  A  strawberry  is  a  very  much 
enlarged  and  fleshy  receptacle,  in  the  surface  of  which 
minute  akenes  are  imbedded  (Fig.  234).  A  blackberry  is 
not  only  a  cylindrical  mass  of  small  stone-fruits,  but  also 
includes  the  fleshy  receptacle. 

In  such  fruits  as  apples,  pears,  and  quinces,  the  fleshy 
part  is  the  modified  cup-like  base  of  the  flower  surrounding 


FIG.  236. — Pineapple  in  surface  view  and  section. 

the  ovary,  which  with  its  contained  seeds  is  represented 
by  the  core  (Fig.  235).  An  extreme  case  is  the  pineapple, 
in  which  a  whole  flower-cluster  has  become  an  enlarged 
fleshy  mass,  including  axis  and  bracts  (Fig.  236). 


CHAPTER  XIV 

FLOWERS   AND   INSECTS 

144.  Pollination. — Among  Gymnosperms  the  pollen  is 
transferred  by  the  wind,  and  this  is  true  also  of  many 
Angiosperms.  But  the  prevailing  method  of  pollination 
among  Angiosperms  is  the  use  of  insects  as  the  agents  of 
transfer.  This  mutually  helpful  relation  between  flowers 
and  insects  is  a  very  remarkable  one,  and  in  some  cases 
it  has  become  so  intimate  that  they  cannot  exist  without 
each  other.  Flowers  are  modified  in  many  ways  in  rela- 
tion to  insect  visits,  and  insects  are  variously  adapted  to 
flowers. 

The  pollen  may  be  transferred  to  the  stigma  of  its  own 
flower  (self-pollination),  or  to  the  stigma  of  some  other 
flower  of  the  same  kind  (cross-pollination).  In  the  latter 
case  the  two  flowers  concerned  may  be  upon  the  same 
plant  or  upon  different  plants,  which  may  be  quite  distant 
from  one  another.  Since  flowers  are  very  commonly  ar- 
ranged to  secure  cross-pollination,  it  must  be  more  advan- 
tageous in  general  than  self-pollination. 

The  advantage  of  this  relation  to  the  insect  is  to  secure 
food.  This  the  flower  provides  in  the  form  of  .either  nectar 
or  pollen;  and  insects  visiting  flowers  may  be  grouped  as 
nectar-feeders,  represented  by  moths  and  butterflies,  and 
pollen-feeders,  represented  by  the  numerous  bees  and  wasps. 
The  presence  of  these  supplies  of  food  in  the  flower  is  made 
known  to  the  insect  by  the  display  of  color,  by  odor,  or  by 
form.  It  should  be  said  that  the  attraction  of  insects  to 
242 


FLOWERS  AND  INSECTS  243 

flowers  by  color  has  been  doubted,  since  it  is  claimed  that 
some  of  the  common  flower-visiting  insects  are  color-blind, 
but  remarkably  keen  of  scent.  However  this  may  be 
for  some  insects,  it  seems  to  be  sufficiently  established  that 
many  insects  recognize  their  feeding  ground  by  the  display 
of  color. 

It  is  evident  that  all  insects  attracted  by  nectar  or  pollen 
are  not  suitable  for  the  work  of  pollination.  For  instance, 
ordinary  ants  are  fond  of  such  food,  but  as  they  walk  from 
plant  to  plant  any  pollen  dusted  upon  them  is  almost  sure 
to  be  brushed  off  on  the  way  and  lost.  The  most  favorable 
insect  is  the  flying  one,  which  can  pass  from  flower  to 
flower  through  the  air.  It  will  be  seen,  therefore,  that  the 
flower  not  only  must  secure  the  visits  of  suitable  insects, 
but  also  must  guard  against  the  depredations  of  unsuitable 
ones. 

145.  Self-pollination. — It  is  evident  that  in  many  cases 
self-pollination  is  likely  to  occur.  In  some  flowers  the  sta- 
mens and  carpels  are  so  related  to  one  another  in  position 
that  when  pollen  is  being  shed  some  of  it  may  fall  upon  the 
stigma.  Even  the  visit  of  an  insect,  which  usually  results 
in  cross-pollination,  may  result  in  self-pollination. 

It  must  not  be  understood  that  only  cross-pollination  is 
really  provided  for,  and  that  when  self-pollination  occurs 
it  is  more  or  less  of  an  accident.  In  addition  to  the  numer- 
ous cases  of  what  may  be  called  accidental  self-polli- 
nation in  flowers  usually  cross-pollinated,  self-pollination  is 
definitely  provided  for  more  extensively  than  once  was 
supposed.  It  is  found  that  many  plants,  as  violets,  for 
example,  in  addition  to  the  usual  showy  insect-pollinated 
flowers,  produce  flowers  that  are  not  at  all  showy,  that  in 
fact  do  not  open,  and  are  often  not  prominently  placed. 
These  inconspicuous  closed  flowers  are  called  cleistogamous 
flowers;  and  in  these  flowers  self-pollination  is  necessary, 
and  very  effective  in  producing  good  seed. 


244 


A   TEXT-BOOK  OF   BOTANY 


146.  Yucca  and  Pronuba. — This  is  a  remarkable  case  of 
self-pollination  by  means  of  an  insect.     Yucca  is   a   plant 

of  the  southwest- 
ern arid  regions 
of  North  America, 
and  Pronuba  is  a 
moth;  and  the  two 
are  very  dependent 
upon  each  other. 
The  bell  -  shaped 
flowers  of  Yucca 
hang  in  great  ter- 
minal clusters.  In 
each  pendent  flower 

FIG.  237.— The  pendent  flower  of   Yucca,   showing     (Fig-   237)  there    are 
position  of  stamens  and  the  ribbed  ovary. — After     gjx        hanging        sta- 

mens,  and  an  ovary 
ribbed  lengthwise,  with  a  fun- 
nel-shaped stigmatic  opening 
in  its  top  (Fig.  238).  The 
numerous  small  ovules  occur 
in  rows  beneath  the  furrows. 


RILEY  and  TRELEASE. 


FIG.  238  — Longitudinal  section  of  an 
ovary  of  Yucca,  showing  the  funnel- 
shaped  stigmatic  opening  (s),  and  the 
rows  of  ovules  attached  to  the  wall 
(o). — After  RILEY  and  TRELEASE. 


FIG.  239. — The  position  of  Pronuba  on 
the  stamen  of  Yucca  when  collecting 
pollen  (.4)  and  when  thrusting  it 
into  the  stigmatic  funnel  (B). — Af- 
ter RILEY  and  TRELEASE. 


FLOWERS  AND   INSECTS 


245 


During  the  day  the  small  female  Pronuba  rests  quietly 
within  the  flower,  but  at  dusk  becomes  very  active.  She 
travels  down  the  stamens,  and  resting  on  an  open  pollen 
sac  scoops  out  the  somewhat 
sticky  pollen  with  her  front  legs 
(Fig.  239,  A).  Holding  the  little 
mass  of  pollen  against  her  body, 
she  runs  to  the  ovary,  stands 
astride  one  of  the  furrows,  and 
piercing  through  the  wall  with 
her  ovipositor  deposits  an  egg 
in  an  ovule.  After  depositing 
several  eggs  in  this  way,  she 
runs  to  the  top  of  the  ovary  and 
begins  to  crowd  into  the  funnel- 
shaped  stigmatic  cavity  the  mass 
of  pollen  she  has  collected  (Fig. 
239,  £).  These  actions  are  re- 
peated several  times,  until  many 
eggs  have  been  deposited  and 
repeated  pollination  has  been 
effected.  As  a  result  of  this, 
seeds  are  formed  which  develop 
abundant  nourishment  for  the 
moth  larvae,  which  become  mature  and  bore  their  way  out 
through  the  wall  of  the  capsule  (Fig.  240). 

147.  Cross-pollination. — In  those  flowers  in  which  cross- 
pollination  is  the  rule,  self-pollination  is  hindered  in  a 
variety  of  ways.  In  the  cases  about  to  be  considered, 
stamens  and  carpels  are  together  in  the  same  flower;  of 
course,  in  dioecious  plants  there  can  be  no  such  thing  as 
self-pollination.  It  is  necessary  to  remember  also  that 
when  the  stigma  is  ready  to  receive  the  pollen,  it  excretes 
upon  its  surface  a  sweetish,  sticky  fluid,  which  holds  and 
feeds  the  pollen,  inducing  the  development  of  pollen  tubes. 


FIG.  240.— A  mature  capsule  of 
Yucca,  showing  perforations 
made  by  larvae  of  Pronuba  in 
escaping.  —  After  RILEY  and 
TRELEASE. 


246 


A  TEXT-BOOK  OF  BOTANY 


In  this  condition  the  stigma  is  said  to  be  ready  or  mature. 
The  pollen  is  mature  when  it  is  ready  to  fall  out  of  the 
pollen  sacs  or  to  be  removed  from  them.  In  obtaining 
nectar  or  pollen  as  food,  the  visiting  insect  receives  pollen 
on  some  part  of  its  body  which  will  be  likely  to  come  in 
contact  with  the  stigma  of  the  next  flower  visited. 

Cross-pollinating  flowers  may  be  illustrated  under  three 
heads,  distinguished  from  one  another  by  their  methods  of 
hindering  self-pollination;  but  it  must  be  understood  that 
almost  every  kind  of  flower  has  its  own  way  of  solving  the 
problems  of  pollination.  It  is  an  exceedingly  interesting 
and  profitable  exercise  for  the  student  to  examine  as  many 
cross-pollinating1  flowers  as  possible,  with  the  view  of  de- 
termining in  each  case  how  self-pollination  is  hindered, 
how  cross-pollination  is  secured,  and  how  the  visits  of 
unsuitable  insects  are  discouraged. 

(1)  Position. — In  these  cases  the  pollen  and  the  stig- 
ma are  ready  at  the  same  time;  but  their  position  in  refer- 
ence to  each  oth- 
er, or  in  reference 
to  some  conforma- 
tion of  the  flower, 
makes  it  unlike- 
ly that  the  pol- 
len will  fall  upon 
the  stigma.  The 
three  following 
illustrations,  se- 
lected from  hun- 
dreds, may  be 
given : 

In  the  family 
(Leguminosce)  to 
which  the  pea, 
bean,  etc.,  belong, 


Fia.  241 . — Rose  aeacia :  A ,  keel  projecting  from  hairy 
calyx,  the  other  petals  having  been  removed;  B, 
protrusion  of  tip  of  style  when  keel  is  depressed  ; 
C.  section  showing  position  of  parts  within  keel. — 
After  GRAY. 


FLOWERS  AND  INSECTS 


247 


the  several  stamens  and  the  single  carpel  are  in  a  cluster 

enclosed  in  a  boat-shaped   structure  (keel)  formed  by  two 

of  the  petals  (Fig.  241).     The  stigma  is  at  the  summit  of 

the  style  and  projects  somewhat  beyond  the   pollen  sacs, 

some    of    whose   pollen   lodges  on   a  hairy   zone  on   the 

style  below  the  stigma.      While  the  stigma   is  not   alto- 

gether secure  from   receiving   some   pollen,  the   position 

does   not   favor  it.     The 

projecting  keel  is  the  nat- 

ural landing  place  for  a 

bee   visiting    the   flower; 

and  it  is  so  inserted  that 

the  weight  of  the  insect 

depresses  it,  and  the  stig- 

ma comes  in  contact  with 

its  body.     Not  only  does 

the     stigma     strike     the 

body,   but   by   the   glan- 

cing blow  the  surface  of 

the  style  is  rubbed  against 

the  insect;  and  upon  this 

style,  below  the   stigma, 

the  pollen  has  been  shed 

and  is  rubbed  off  against 

,         .  .          , 

the    insect.       At    the    next 

flower   Visited    the   Stigma 
IS  likely  to  Strike  the  pol- 

len  obtained  from  the  pre- 


FIG.  242.— Longitudinal  section  of  flower  of 
iris,  showing  a  single  stamen  between  the 
drooping  petal  and  the  petal-like  style; 
the  stigmatic  shelf  is  seen  above  the 
stamen,  at  the  top  of  the  style;  the  nectar 


vious  flower,  and  the  style 

will  deposit  a  new  supply  of  pollen.  It  is  interesting  to 
press  down  slightly  the  keel  of  such  a  flower  and  see  the 
style  apparently  dart  out. 

In  the  iris  or  common  flag,  each  stamen  is  in  a  kind  of 
pocket  between  the  petal  and  the  petal-like  style;  while 
the  stigmatic  surface  is  on  the  top  of  a  flap  or  shelf  which 
17 


248 


A  TEXT-BOOK  OF  BOTANY 


the  style  sends  out  as  a  roof  to  the  pocket  (Fig.  242). 
With  such  an  arrangement  it  would  seem  impossible  for  the 
pollen  to  reach  the  stigma  unaided.  The  nectar  is  in  a 

little  pit  at  the  bottom  of 
the  pocket.  As  the  insect 
crowds  its  way  into  the  nar- 
rowing pocket,  its  body  is 
dusted  by  the  pollen;  and 
when  it  visits  the  next 
flower,  and  pushes  aside  the 
stigmatic  shelf,  it  is  likely 
to  deposit  upon  it  some  of 
the  pollen  previously  re- 
ceived. 

In  the  orchids,  remark- 
able for  their  strange  and 
beautiful  flowers,  the  story 
of  pollination  is  still  more 
complicated.  There  are 
usually  two  pollen  sacs,  and 
the  pollen  grains  are  not 
dry  and  powdery,  but  cling 
together  in  a  mass  (pollin- 
iwri),  which  must  be  pulled 
out  bodily.  An  illustration 
of  a  common  method  of 


PIG.  243.  —  Flower  of  rein  orchis:  A,  com- 
plete flower,  showing  three  broad  se- 
pals, three  narrower  petals  (one  of 
which  forms  the  long  lip  and  the  much 

longer  spur),  two  pollen  sacs,  between    pollination  may  be  obtained 

which  extends  the  concave  stigmatic 

surface  (at  the  bottom  of  which  the 

opening  to  the  tube  is  seen);  B,  more      chis  (Fig.  243). 

enlarged  view  of  pollen  sacs,  stigmatic 

surface,  and  buttons  ;  C,  a  pollinium 


11 
tWO      pollen 


rpn    nr- 
Each  of  the 
maSSCS     termi- 


removed;  D,  a  button  enlarged.—  Af-     nates     in     a     Sticky     disk    Or 
ter  GRAY. 

button;  and  between  them 

extends  the  concave  stigmatic  surface,  at  the  bottom  of 
which  is  the  opening  into  the  long  tube-like  spur  in  the 
bottom  of  which  the  nectar  is  found.  Such  a  flower  is 


FLOWERS  AND  INSECTS 


249 


adapted  to  the  large  moths,  with  long  proboscides  which 
can  reach  the  bottom  of  the  tube.  As  the  moth  thrusts 
its  proboscis  into  the  tube,  its  head  is  pressed  against 
the  sticky  button  on  each  side,  so  that  when  it  flies  away 
these  buttons  stick  to  its  head  and  the  pollen  masses  are 
torn  out.  When  the  next  flower  is  visited  these  pollen 
masses  are  thrust  against  the  stigmatic  surface. 

(2)  Consecutive  maturity. — In  these  cases  pollen  and  stig- 
ma of  the  same  flower  are  not  mature  at  the  same  time. 
This  is  a  common  method  of  preventing  self-pollination, 
and  it  is  evident  that  it  is  effective.  When  the  pollen  is 
being  shed,  the  stigma  is  not  ready  to  receive;  or  when  the 
stigma  is  ready  to  receive,  the  pollen  is  not  ready  to  be 
shed. 

When  the  flowers  of  the  ordinary  figwort  first  open,  the 
style  bearing  the  stigma  at  its  tip  is  found  protruding 


B  C 

FIG.  244. — Protogynous  flower  of  figwort:  .4,  first  stage,  with  stigma  receptive; 
B,  section  of  A,  showing  stamens  within  the  corolla;  C,  second  stage,  with 
stigma  past  and  anthers  in  position  for  shedding. — After  GRAY. 

from  the  urn-like  flower,  while  the  four  stamens  are  curved 
down  into  the  tube,  and  are  not  ready  to  shed  their  pollen 
(Fig.  244,  A  and  B}.  At  some  later  time,  the  style  bearing 
the  stigma  wilts,  and  the  stamens  straighten  up  and  pro- 
trude from  the  tube  (Fig.  244,  C).  In  this  way,  first  the 


250 


A  TEXT-BOOK  OF  BOTANY 


receptive  stigma,  and  afterward  the  shedding  pollen  sacs 
occupy  the  same  position.  A  visiting  insect  will  probably 
find  flowers  in  both  conditions;  and,  while  striking  against 
protruding  and  shedding  pollen  sacs  in  some  flowers,  it 
strikes  against  a  protruding  stigma  in  other  flowers,  and 
thus  carries  pollen  from  one  to  the  other.  Such  flowers 
are  called  protogynous ,  which  means  "pistil  first." 

More  frequently,  however,  flowers  are  protandrous, 
which  means  "stamens  first."  For  example,  when  the 
showy  flowers  of  the  common  fireweed,  or  great  willow  herb, 
first  open,  the  eight  shedding  stamens  project  prominently, 
the  style  being  sharply  curved  downward  and  backward, 
carrying  the  stigmatic  lobes  well  out  of  the  way  (Fig.  245, 
A).  Later,  the  stamens  bend  away  and  the  style  straightens 


A  B 

FIG.  245. — Protandr&us  flower  of  willow  herb:  A,  first  stage,  with  anthers  in  posi- 
tion for  shedding  and  style  curved  downward;  B,  second  stage,  with  anthers 
past  and  stigmatic  lobes  in  position  for  receiving  pollen. — After  GRAY. 

up  and  exposes  the  stigma  (Fig.  245,  B).  The  result  of  the 
visits  of  an  insect  is  the  same  as  in  the  case  of  the  pro- 
togynous flowers.  So  many  cases  of  protandrous  flowers 
occur  among  common  wild  and  cultivated  plants  that 
illustrations  should  be  discovered  easily. 

(3)  Difference  in  pollen. — In  these  cases  there  are  gen- 
erally two  forms  of  flowers,  which  differ  from  each  other 
in  the  relative  lengths  of  tneir  stamens  and  styles.  In 
the  accompanying  illustration  it  will  be  seen  that  in  one 


FLOWERS  AND   INSECTS  251 

flower  the  stamens  are  short  and  included  in  the  tube, 
while  the  style  is  long  and  projecting,  with  the  four  stig- 
matic  lobes  exposed  well  above  the  corolla  (Fig.  246,  A). 


A 

FIG.  246. — Flowers  of  Houatonia:  A,  form  with  short  stamens  and  long  style;  B, 
form  with  long  stamens  and  short  style. — After  GRAY. 

In  the  other  flower  the  relative  lengths  are  exactly  reversed, 
the  style  being  short  and  included  in  the  tube,  and  the 
stamens  long  and  projecting  (Fig.  246,  B).  It  appears 
that  the  pollen  from  the  short  stamens  is  more  effective 
upon  the  short  style;  and  that  the  pollen  from  the  long 
stamens  is  more  effective  upon  the  long  style.  The  body 
of  the  visiting  insect  fills  the  corolla  tube  and  projects 
above  it.  In  visiting  flowers  of  both  kinds,  one  region  of 
the  body  receives  pollen  from  the  short  stamens,  and 
another  region  from  the  long  stamens.  In  this  way  the 
insect  is  soon  carrying  about  two  bands  of  pollen,  which 
come  in  contact  with  corresponding  stigmas. 


252 


A  TEXT-BOOK  OP  BOTANY 


148.  Figs. — Perhaps  the  most  remarkable  case  of  an 
intimate  relationship  between  insects  and  flowers  is  that 
which  exists  between  a  small  wasp  (Blastophaga)  and  the 
cultivated  fig.  The  full  story  is  too  intricate  and  variable 
for  presentation  here,  but  a  very  general  outline  may  give 
some  little  idea  of  the  situation.  The  flowers  of  the  fig 
are  borne  in  a  very  peculiar  way.  What  is  called  a  fig  is  a 
hollow  structure  (Fig.  247,  A],  completely  closed  except 

for  a  minute  open- 
ing at  the  top,  and 
bearing  small  flow- 
ers in  large  num- 
bers upon  the  inner 
wall  (Fig.  247,  B). 
Figs  are  dioecious, 
so  that  some  trees 
bear  only  figs  with 
staminate  flowers 
(Fig.  247,  C),  and 
others  only  figs 
with  pistillate  flow- 

FIG.  247.— The  fig:  A,  branch  bearing  a  fig;  B,  sec-      erS     (Fig.     247,    D). 

The  fig  that  has 
been  cultivated  for 
very  many  centuries  in  countries  about  the  Mediterranean 
is  the  pistillate  tree.  In  order  to  make  it  fruit  properly, 
fig-bearing  branches  from  staminate  trees  are  hung  in  the 
pistillate  trees.  These  staminate  figs  were  called  "wild 
figs"  or  ca'prifigs,  and  the  process  of  placing  them  on  the 
pistillate  tree  was  called  caprification. 

Only  in  recent  times  has  the  meaning  of  this  very 
ancient  process  become  known.  As  the  plants  are  dioecious, 
caprification  is  evidently  bringing  the  staminate  flowers 
near  enough  to  the  pistillate  flowers  to  secure  a  transfer  of 
the  pollen.  As  both  kinds  of  flowers  are  enclosed  in  the  fig, 


tion  of  fig  showing  flowers  within;    C,  staminate 
flower ;  D,  pistillate  flower. — After  WOSSIDLO. 


FLOWERS  AND  INSECTS  253 

it  is  evident  that  neither  the  wind  nor  an  ordinary  insect 
can  transfer  the  pollen.  This  is  effected  by  the  small  fig 
wasp  that  passes  its  whole  existence  within  the  figs.  Its 
real  home  is  the  staminate  fig  (caprifig),  and  there  it 
deposits  its  eggs  and  dies.  The  new  generation  of  fig 
wasps  crawl  out  of  the  old  fig,  and  entering  another  one 
that  is  young  deposit  their  eggs  and  die,  and  so  on.  A 
staminate  fig-tree  usually  bears  three  crops  of  caprifigs  each 
year,  the  troe  never  being  without  a  crop;  and  so  three 
generations  of  fig  wasps  are  produced  in  the  year,  and  there 
is  always  a  home  for  them. 

When  a  branch  bearing  staminate  figs  is  placed  in  a 
tree  bearing  pistillate  ones,  the  young  wasps  crawling  out 
of  the  former  enter  the  latter,  which  at  this  stage  closely 
resemble  the  caprifigs.  Having  entered,  the  wasps  find 
themselves  in  a  trap,  for  the  flower  structures  are  such  that 
they  cannot  deposit  eggs  properly.  But  their  bodies  are 
covered  with  pollen  from  their  former  home,  and  running 
about  among  the  pistillate  flowers  they  pollinate  them  very 
completely.  As  a  consequence,  the  pistillate  fig  ripens, 
forms  numerous  seeds,  and  acquires  the  peculiar  nutty 
flavor  that  characterizes  it. 

Pistillate  figs  ripen  without  this  process,  but  they  do 
not  set  seed  nor  acquire  the  characteristic  flavor,  nor  can 
they  be  dried  for  shipping.  They  can  only  be  used  as 
fresh  figs,  and  are  not  at  all  the  ordinary  figs  of  commerce, 
known  as  Smyrna  figs.  During  the  last  years  of  the  past 
century  the  United  States  Department  of  Agriculture, 
after  several  failures,  succeeded  in  introducing  the  fig  wasp 
into  California,  so  that  real  Smyrna  figs  are  now  being 
grown  in  our  own  country. 

149.  Hybrids. — In  the  transfer  of  pollen  by  wind  and 
insects,  some  of  it  may  reach  stigmas  belonging  to  a  differ- 
ent kind  of  plant.  If  this  plant  is  nearly  related  to  the  one 
that  has  produced  the  pollen,  fertilization  may  result. 


254  A  TEXT-BOOK  OF  BOTANY 

When  the  seeds  formed  in  this  way  germinate,  they  produce 
plants  that  are  called  hybrids]  that  is,  plant's  whose  two 
parents  belong  to  different  species  or  races.  The  hybrid 
usually  shows  some  combination  of  the  characters  of  both 
parents,  but  it  may  be  very  different  from  either. 

In  this  way  new  kinds  of  plants  often  arise  in  nature, 
and  advantage  is  taken  of  this  fact  to  produce  new  forms  in 
cultivation.  This  cross-pollination  between  plants  of  differ- 
ent kinds,  resulting  in  cross-fertilization,  is  usually  spoken 
of  simply  as  crossing,  and  the  use  of  crossing  in  producing 
new  forms  will  be  spoken  of  more  fully  in  the  chapter  on 
plant  breeding.  An  illustration  of  what  is  meant  by  hybrids 
may  be  obtained  from  corn.  There  are  several  races  of 
corn  that  differ  in  the  color  of  the  grains,  which  are  white, 
yellow,  red,  or  lead-colored.  If  a  white  race  be  crossed 
with  a  red  race,  the  resulting  ears  will  be  hybrids,  and  will 
very  likely  show  both  colors  in  the  same  ear.  When  the 
grains  are  sown  and  produce  new  plants,  these  plants  are 
hybrids  and  will  show  resemblances  to  both  parents. 


CHAPTER  XV 

SEED-DISPERSAL 

150.  Reasons  for  dispersal. — If  all  seeds  dropped  about 
the  parent  plants,  there  soon  would  not  be  room   enough 
for  any  more  to  grow,  and  those  that  did  grow  would  in- 
terfere  with   one  another  seriously.     It  is  of  advantage 
both  to  the  parent  plant  and  to  the  young  plants  for  the 
seeds  to  be  scattered  beyond  the  reach  of  such  rivalry. 
Accordingly,  there  are  many  ways  by  which  seeds  are  dis- 
persed, and  sometimes  they  are  carried  to  great  distances. 
When  fruits  open  to  discharge  seeds,  the  seeds  themselves 
are  scattered;  but  when  fruits  do  not  open,  the  fruit  itself 
is  transported. 

151.  Dispersal  by  discharge. — In  some  plants  there  is  a 
mechanical  discharge  of  seeds  provided  for  in  the  structure 
of   the    seed-vessel,   such  t 

fruits  often   being  called 


FIG.  248.— The   fruit  of  violet  dig-        FIG.  249.— The  pods  of  a  wild  bean  (Lotus) 
charging    seeds.  —  After    BAIL-  twisting   in   discharging   seeds.  —  After 

LON.  BA.ILLON. 

255 


256 


A  TEXT-BOOK   OF  BOTANY 


sling-fruits.  In  the  violet  and  the  witch-hazel,  when  the 
seed-vessel  splits,  its  walls  press  upon  the  seeds  so  that  they 
are  pinched  out,  as  a  moist  apple-seed  is  projected  by  being 
pressed  between  the  thumb  and  the  finger  (Fig.  248). 
When  the  pod  of  the  wild  bean  bursts,  the  two  valves  twist 

violently  and  throw 
the  seeds  (Fig.  249). 
In  the  touch-me- 
not,  or  the  balsam, 
a  strain  is  devel- 
oped in  the  grow- 
ing wall  of  the 
seed-vessel,  so  that 
at  rupture,  which 
may  be  brought 

FIG.  250.— Winged  fruit  of  maple.— After  KEENER.         about        by       slight 

pressure,  the  pieces 

suddenly  curl  up  and  throw  the  seeds.  The  squirting 
cucumber  is  so  named  because  it  becomes  very  much 
distended  with  water,  which  is  finally  forcibly  ejected 


FIG.  251. — Winged  seed  of  Bignonin. — After  STRASBTTRGER. 

along  with  the  mass  of  seed.  In  tropical  forests  there 
are  plants  whose  large  seed-vessels  explode  with  a  loud 
report. 


SEED-DISPERSAL 


257 


This  method  may  be  regarded  as  the  poorest  of  all  the 
methods  of  dispersal,  for  at  the  very  best  no  seed-vessel 
can  discharge  its  seeds  more  than  a  very  short  distance. 

152.  Dispersal  by  currents  of  air. — Many  seeds  are  so 
light  as  to  be  carried  about  by  currents  of  air.  Ordinarily, 
however,  the  wind-dispersed  seeds  or  fruits  develop  special 
appendages  to  aid  in  their  flight,  commonest  among  which 

are  wings  and  tufts  of  hair. 
For  example,  wings  are  de- 
veloped by  the  fruit  of  ma- 
ples (Fig.  250)  and  elms,  and 
by  the  seeds  of  catalpa  and 
its  allies  (Fig.  251).  Plumes 
and  tufts  of  hair  are  devel- 


FIG.    252. — Akenes   of   dandelion   with 
tufts  of  hair. — After  KEENER. 


FIG.  253. — Akenes  of  Senecio  with  tufts 
of  hair. — After  KEENER. 


oped  by  the  seed-like  fruits  of  thistle,  dandelion  (Fig. 
252),  and  many  of  their  relatives  (Fig.  253);  and  by  the 
seeds  of  milkweeds  (Fig.  254),  willow  herbs  (Fig.  255),  etc. 
On  plains,  or  level  stretches,  where  winds  are  strong,  a 
curious  habit  of  seed-dispersal  has  been  developed  by 
certain  plants  known  as  tumbleweeds  or  field  rollers  (Fig. 
256).  These  plants  are  profusely  branching  annuals  with 


258 


A  TEXT-BOOK  OF  BOTANY 


a  small  root  system  in  light  or  sandy  soil.  When  the  work 
of  the  season  is  over,  and  the  absorbing  rootlets  have 
shriveled,  the  plant  is 
easily  broken  from  its 


FIG.  254. — Seed  of  milkweed  with 
tuft  of  hair. — After  GRAY. 


FIG.    255.- 


-Seed  of  willow  herb  with   tuft 
of  hair. 


FIG.  256. — A  common  tumbleweed. 


SEED-DISPERSAL  259 

roots  by  a  gust  of  wind,  and  is  trundled  along  the  surface 
like  a  light  wicker  ball,  the  ripe  seed-vessels  dropping  their 
seeds  by  the  way.  In  case  of  an  obstruction,  such  as  a 
fence,  great  masses  of  these  tumble  weeds  may  be  seen 
lodged  against  the  windward  side. 

This  method  of  dispersal  is  far  more  effective  than  the 
mechanical  discharge;  but  it  is  fitful,  and  its  range  usually 
is  not  very  great.  Thistle-down  may  be  floated  into  a 
neighboring  field,  and  a  strong  wind  may  carry  the  com- 
paratively heavy-winged  fruits  of  the  maple  and  the  elm 
some  distance;  but  at  best  the  scattering  is  only  over  a 
neighborhood. 

153.  Dispersal  by  currents  of  water. — Many  seeds  are 
buoyant,  or  become  so  after  soaking  in  water,  and  may  be 
carried  great  distances  by  currents.  For  example,  the 
banks  and  flood-plains  of  streams  may  receive  seeds  from 
a  wide  area,  dependent  on  the  extent  of  the  drainage  system. 
Along  the  lower  stretches  of  rivers  such  as  the  Mississippi, 
the  Missouri,  or  the  Ohio,  almost  every  season  new  plants 
are  added  to  those  growing  along  the  banks,  and  some 
of  them  may  have  come  from  great  distances.  This  kind 
of  distribution,  therefore,  may  become  almost  continental 
in  extent. 

Still  more  far-reaching  is  the  dispersal  brought  about 
by  oceanic  currents,  both  by  waves  carrying  seeds  along 
the  coast,  and  also  by  the  deeper  currents  that  extend 
from  continent  to  continent  or  to  oceanic  islands.  It  has 
been  found  that  many  seeds  can  endure  even  prolonged 
soaking  in  sea-water  and  then  germinate.  From  a  series 
of  experiments,  Darwin  estimated  that  at  least  fourteen 
per  cent  of  the  seeds  of  British  plants  can  retain  their 
vitality  in  sea- water  for  twenty-eight  days.  At  the 
ordinary  rate  of  movement  of  ocean  currents,  this  length 
of  time  would  permit  seeds  to  be  transported  over  a  thousand 
miles.  It  is  thought  that  the  appearance  on  islands  of 


260 


A   TEXT-BOOK  OF  BOTANY 


certain  plants  belonging  to  an   adjacent   continent   may 

often  be  explained  in  this  way. 

154.  Dispersal   by  animals.  —  Only   a   few  illustrations 

of  this  very  large  subject  can  be  given.  Water-birds  are 
great  carriers  of  seeds,  which  are  con- 
tained in  the  mud  clinging  to  their  feet 
and  legs.  This  mud  from  the  borders  of 
ponds  is  usually  completely  filled  with 
seeds  of  various  plants.  One  has  no  con- 
ception of  the  number  until  it  is  actually 
computed.  The  following  extract  from 
Darwin's  Origin  of  Species  illustrates  this 
point  : 

"I  took,  in  February,  three   tablespoonfuls  of 
mud  from  three  different  points  beneath  the  water, 
on    the    edge  of  a  little  pond. 
The  mud  when   dried   weighed 
FIG    257.  —  Akene    only  6  1  ounces;  I  kept   it  cov- 
of    Spanish    nee-     ered     up    in    my    study    for    six 
dies  with  barbed 

appendages.-Af-    weeks>  pulling  up  and  counting 

ter  KEENER.  each  plant  as  it  grew;  the  plants 

were  of  many  kinds,  and    were 

altogether  537  in  number;  and  yet  the  viscid  mud 

was  all  contained  in  a  breakfast  cup!" 


Water-birds  are  generally  high  and 
strong  fliers,  and  the  seeds  may  be  trans- 
ported thus  to  the  margins  of  distant 
ponds  and  lakes,  and  so  become  very 
widely  dispersed. 

In  many  cases  seeds  or  fruits  or  heads 
develop  grappling  appendages  of  various 
kinds,  forming    the   various   burs,   which      barbed  appendages. 
lay  hold  of  animals   brushing  past;   and 
so    the    seeds   are    dispersed.      Common    illustrations    of 
fruits    with    grappling    appendages    are    Spanish    needles 


SEED-DISPERSAL  261 

(Fig.  257),  beggar-ticks  (Fig.  258),  stick  seeds,  etc.;  and 
similar  appendages  are  developed  in  connection  with  the 
involucres  of  cockle-bur 
(Fig.  259,  A),  burdock 
(Fig.  259,  B),  etc. 

Fleshy  fruits  are  at- 
tractive as  food  to  cer- 
tain birds  and  mam- 
mals. Many  of  the 
seeds  (such  as  those  of  A 

grapes)   may  be    able    tO     FIG.  259.— Heads  of  cockle-bur  (A)  and  burdock 

resist  the  attacks  of  the  ^0i^.-\^K^^nd&ge9  °f  the 
digestive  fluids  and  es- 
cape from  the  alimentary  tract  in  a  condition  to  germi- 
nate. As  if  to  attract  the  attention  of  fruit-eating  ani- 
mals, fleshy  fruits  usually  become  brightly  colored  when 
ripe,  so  that  they  are  plainly  seen  in  contrast  with  the 
foliage, 


CHAPTER  XVI 

MONOCOTYLEDONS 

155.  Classification. — The  Angiosperms  are  so  numerous 
that  it  requires  much  time  through  several  seasons  to  get 
acquainted  fairly  well  with  them  in  any  one  neighborhood. 
The  elementary  student  should  begin  at  once  to  cultivate 
this  acquaintance  by  learning  to  recognize  the  most  promi- 
nent groups  and  the  most  common  representatives  of  each 
group.  For  example,  there  should  be  no  difficulty  usually 
in  recognizing  whether  a  given  plant  is  a  Monocotyledon  or  a 
Dicotyledon;  since  the  floral  number,  the  venation,  and  the 
stem  arrangement  of  vascular  bundles  will  determine  that 
in  most  cases. 

In  each  of  these  two  great  divisions  of  Angiosperms, 
however,  there  are  numerous  families,  and  one  should  be- 
come acquainted  early  with  the  most  conspicuous  families 
of  a  neighborhood.  For  example,  a  very  conspicuous 
family  of  the  Monocotyledons  in  every  neighborhood  is 
that  which  contains  the  grasses;  but  in  every  neighbor- 
hood there  will  occur  also  ten  to  twenty  other  prominent 
families  of  Angiosperms  that  deserve  recognition. 

A  family  is  made  up  of  smaller  groups  called  genera 
(singular  genus).  For  example,  in  the  great  family  to 
which  the  asters  belong,  the  different  asters  resemble 
one  another  more  than  they  do  any  other  members  of  the 
family;  and  so  there  is  the  aster  genus.  In  the  same  family 
the  different  goldenrods  are  grouped  together  in  a  golden- 
rod  genus.  The  different  kinds  of  aster  or  of  goldenrod 


MONOCOTYLEDONS  263 

are  called  species.  Therefore,  a  group  of  related  species 
forms  a  genus;  and  a  group  of  related  genera  forms  a  family. 
An  acquaintance  with  the  plants  of  a  neighborhood  should 
begin  by  learning  to  recognize  not  merely  important  families 
but  also  conspicuous  and  common  genera  and  species. 

The  technical  name  of  a  plant  is  the  combination  of  its 
generic  and  specific  names,  the  former  always  being  written 
first.  For  example,  Quercus  alba  is  the  name  of  the  com- 
mon white  oak,  Quercus  being  the  name  of  the  genus  to 
which  all  oaks  belong,  and  alba  the  specific  name  that 
distinguishes  this  oak  from  other  oaks.  No  other  names 
are  necessary,  as  no  two  genera  of  plants  can  bear  the  same 
name,  and  no  two  species  of  a  genus  can  have  the  same 
name. 

The  so-called  Manuals  or  Keys  are  books  that  contain 
descriptions  of  plants,  so  arranged  that  one  who  knows 
the  meaning  of  the  terms  used  can  find  the  name  of  any 
plant  described.  Ability  to  use  such  a  manual  is  very 
desirable  to  cultivate,  for  it  is  the  most  accurate  and 
effective  method  of  forming  a  speaking  acquaintance  with 
plants. 

156.  Families  of  Monocotyledons. — About  forty  mono- 
cotyledonous  families  are  recognized,  containing  numerous 
genera  and  about  twenty  thousand  species.     Four  fami- 
lies will  be  selected,  which  include  the  great  majority  of 
Monocotyledons;  and  these  should  be  recognized  at  sight. 
These  families  are  conspicuous  in  numbers,  or  in  appearance 
or  in  usefulness;  and  for  any  or  all  of  these  characters  they 
deserve  acquaintance. 

157.  Grasses. — The  Grass  Family  (Graminece)  is  one  of 
the  largest  groups  of  plants.     It  is  world-wide  in  its  dis- 
tribution, and  is  remarkable  in  its  display  of  individual 
plants,  often  growing  so  densely  over  large  areas  as  to  form 
a  close  turf. 

The  flowers  are  very  simple  having  no  calyx  or  corolla, 

18 


A  TEXT-BOOK  OP  BOTANY 


and  the  grain  is  the  characteristic  seed-like  fruit.  The 
flowers  occur  in  small  close  clusters,  and  associated  with 
them  are  peculiar  bracts  characteristic  of  the  family 
(Fig.  260).  For  example,  these  bracts  form  the  so-called 

chaff  of  wheat  and  other 
cereals,  where  they  persist 
and  more  or  less  envelop 
the  grain.  These  little 
clusters  of  bracteate  flow- 
ers are  arranged  to  form 
either  a  loose  and  spread- 
ing general  cluster,  as  in 
red  top  and  oats  (Fig. 
262),  or  else  a  compact, 
spike-like  cluster,  as  in 
timothy  and  wheat  (Fig. 
261). 

When  the  uses  of 
grasses  are  considered,  it 
becomes  evident  that  this 
is  by  far  the  most  impor- 
tant family  of  plants  to 
man.  It  is  possible  to 
suggest  only  some  of  the 
conspicuous  forms. 

(1)  CEREALS. — This  group  includes  those  grasses  that 
are  cultivated  for  their  seed-like  fruits  or  grains,  and  they 
represent  the  chief  interest  of  agriculture.  What  cereals 
mean  as  a  food-supply  for  the  world  is  too  well  known  to 
need  explanation.  The  most  extensively  cultivated  cereals 
are  as  follows: 

Wheat. — This  is  certainly  the  best  known  and  most 
valuable  of  all  cereals.  The  original  home  of  wheat  is 
unknown,  for  it  has  been  cultivated  from  the  very  earliest 
times.  It  is  a  crop  peculiarly  adapted  to  regions  of  cold 


FlQ.  260. — Oats :  A,  part  of  a  flower-cluster, 
showing  the  bracts,  in  the  axils  of  which 
flowers  appear ;  B,  a  single  flower,  with 
its  enveloping  bract,  three  stamens,  and 
pistil  whose  ovary  bears  two  plumose 
styles. — After  BAILLON. 


MONOCOTYLEDONS 


265 


winters,  and  hence  the  greatest  supply  comes  from  temper- 
ate regions.  The  Northern  United  States  and  Canada  have 
vast  areas  especially  well-adapted  to  the  cultivation  of 
wheat;  and  in  1899  (last 
census)  the  United  States 
alone  produced  more  than 
one-fourth  of  the  wheat  of 
the  world,  being  the  great- 
est wheat-producing  coun- 
try. In  this  production 
the  chief  wheat-growing 
States,  in  the  order  of  their 
output,  were  Minnesota, 
North  Dakota,  Ohio,  and 
South  Dakota. 

The  varieties  of  wheat 
are  very  numerous,  and 
new  ones  are  constantly 
being  produced  in  the 
effort  to  get  the  very  best 
variety  for  every  combina- 
tion of  climate  and  soil. 
There  are  spring  and  win- 
ter wheats,  bearded  and 
beardless  wheats  (Fig. 
261),  soft  and  hard  wheats, 
and  wheats  of  various  col- 
ors. Winter  wheat  is  sown  in  the  fall,  and  hence  must 
be  a  variety  able  to  endure  the  winter;  while  spring  wheat 
is  sown  as  early  in  the  spring  as  possible.  Since  wheat 
grows  best  during  the  cool  part  of  the  year,  it  is  very 
conveniently  related  to  the  corn  crop,  which  makes  its 
chief  growth  during  the  warm  months.  The  time  of  har- 
vesting varies  with  the  latitude,  ranging  from  early  in 
May  in  Texas  to  August  in  some  northern  States. 


L 


Fiu.  201. — Bearded  and  beardless  wheat. 
—After  ENGLER  and  PRANTL. 


266 


A  TEXT-BOOK  OF  BOTANY 


Oats. — Oats  may  be  distinguished  from  wheat,  rye,  and 
barley  by  the  flower  clusters  being  loose  and  spreading  (Fig. 
262),  rather  than  in  compact  cylindrical 
clusters  (spikes).  It  also  has  been  culti- 
vated from  the  most  ancient  times,  and 
to-day  the  United  States  and  Russia  pro- 
duce the  greatest  crops.  Oats  are  usually 
sown  as  early  in  the  spring  as  possible, 
developing  best  in  the  cooler  weather; 
and  in  northern  latitudes  the  crop  ma- 
tures in  ninety  days  or  less.  Oats  do 
not  require  so  rich  soil  as  wheat,  and 


FIG.  262.— Oats. 
After  BAILLON. 


hence  can  be  grown 
successfully  where 
wheat  would  not 
thrive.  In  1899  the 
United  States  pro- 
duced more  bush- 
els of  oats  than  of 
wheat. 

Rye. — This  cere- 
al does  not  seem  to 
have  been  so  long 
in  cultivation  as  the 


FIG.  263.— Rye 


MONOCOTYLEDONS 


267 


others  (Fig.  263).     It  is  extensively  cultivated  in  Northern 
Europe;  and  Russia  is  the  greatest  rye-producing  country 
in  the  world,  producing  more  bushels  of  rye  than  the  United 
States  produces  bushels  of  wheat.     The  rye  crop  of  the 
United  States  is  very  small  comparatively,  being  less  than 
one-twenty-fifth  as  large  as  the  wheat  crop,  and  less  than 
one-thirtieth  as  large  as   the  oat  crop.     <Rye  can  grow  in 
regions  too  cold  for  wheat  and  on     _______ __ 

soils  too  poor  for  any  other  grain; 
in  fact  it  does  not  thrive  well  in 
rich  soils.  There  are  spring  and 
winter  varieties.  The  latter  is  the 
one  chiefly  cultivated,  being  sown 
in  the  fall  and  harvested  usually  in 
June. 

Barley. — This  is  one  of  the  most 
ancient  of  cereals  in  cultivation; 
and,  as  it  grows  wild  in  western 
Asia,  this  is  thought  to  be  its 
original  home  (Fig.  264).  It  grows 
through  a  greater  range  of  lati- 
tude than  any  other  cereal,  its  cul- 
tivation extending  from  Iceland 
and  Norway  to  India.  It  demands 
in  general  the  well-prepared  and 
well  -  drained  soil  necessary  for 
wheat.  Its  growing  period  is 
shorter  than  that  of  wheat,  for 
it  is  very  common  to  sow  it  after 
and  to  harvest  it  just  before  spring  wheat.  In  the  United 
States  the  barley  crop  in  1899  was  nearly  three  times  as 
great  as  that  of  rye,  California  producing  more  than  one- 
fourth  of  it,  and  Iowa,  Minnesota,  and  Wisconsin  following 
in  order.  While  barley  is  used  in  feeding,  as  grain,  hay, 
and  straw,  its  most  conspicuous  use  is  by  brewers  in  the 


268 


A  TEXT-BOOK  OP  BOTANY 


process  of  malting;  and  the  best  malting  barley  in  the 
world  is  grown  in  eastern  England. 

Corn. — Indian  corn,  or  maize  as  it  should  be  called,  is 
peculiarly  an  American  crop  (Fig.  265).     It  is  thought  to 

be  of  American  origin  and 
was  cultivated  by  the  native 
tribes  long  before  the  coming 
of  Europeans;  and  four-fifths 
of  the  corn  of  the  world  is  still 
produced  in  the  United  States. 
The  plant  varies  in  height  from 
dwarf  varieties  less  than  two 
feet,  to  large  varieties  fifteen 
or  twenty  feet  in  river  bot- 
toms, and  even  thirty  feet  and 
more  is  reported  from  the  West 
Indies.  The  staminate  and  pis- 
tillate flowers  occur  in  separate 
clusters  on  the  same  stalk;  that 
is,  the  plant  is  monoecious. 
The  staminate  cluster  is  at 
the  top,  and  is  called  the  tas- 
sel; while  the  pistillate  clus- 
ters (ears),  with  their  enveloping  bracts  (husks),  occur  in 
the  axils  of  leaves,  the  long  styles  forming  the  so-called  silk. 
The  prominent  groups  of  corn  are  dent  corn,  flint  corn, 
sweet  corn,  and  pop-corn;  and  each  of  these  has  many 
varieties,  differing  in  certain  qualities  and  also  in  color, 
white  or  yellow  grains  prevailing.  Most  of  the  field  corn 
produced  in  the  United  States  is  dent  corn,  recognized  by 
the  indentation  at  the  top  of  the  grain.  The  best  soil  for 
corn  is  a  rich  loam  that  does  not  bake  during  drought, 
the  plowing  being  deeper  than  for  any  other  grain.  Most 
of  the  world's  corn  is  produced  in  the  northern  States  of 
the  Mississippi  Valley;  and  there  planting  is  done  in  May, 


FIG.  265.— Corn.— After  ENGLER 
and  PRANTL. 


MONOCOTYLEDONS 


269 


and  the  crop  matures  in  about  five  months.  The  great 
corn-producing  States  in  their  order  are  Illinois,  Iowa,  Kan- 
sas, Nebraska,  Missouri,  and  Indiana;  and  in  1899  these 
States  produced  nearly  three-fifths  of  the  entire  crop  of  the 
United  States. 

Aside  from  its  use  as  a  food  for  man  and  domestic 
animals,  corn,  it  is  said,  enters  into  the  preparation  of 
more  than  a  hundred  different  articles,  in  which  the  husks, 
the  outer  part  of  the  stalk,  the  pith,  and  the  cobs  are  used. 
Most  of  the  starch  of  the  United  States  comes  from  corn, 
and  much  of  the  whisky  and  the  alco- 
hol. In  addition  to  the  various  races 
of  field  corn,  the  sugar-containing  sweet 
corn,  used  in  marketing  and  canning, 
with  its  wrinkled  grains  and  short  grow- 
ing period,  is  well  known;  and  also  the 
small-eared  and  flinty  pop-corn. 

While  corn  is  not  seriously  injured 
by  rusts  (§  84)  as  are  the  other  cere- 
als, its  most  common  disease  is  smut, 
which  appears  as  tumor-like  swellings 
(on  stalks,  leaves,  and  ears)  full  of 
spores  that  look  like  black  powder. 
Smuts  are  related  to  the  rusts,  and 
their  attack  on  corn  has  not  been  pre- 
vented so  successfully  as  have  their 
attacks  on  other  cereals. 

Rice. — Rice  is  said  to  form  the  prin- 
cipal food  of  one-half  the  human  race 
(Fig.  266).  A  native  of  the  East  Indies, 
it  is  cultivated  now  wherever  the  proper 
conditions  are  present.  It  needs  a  sub- 
tropical climate,  and  a  moist  soil  that 
can  be  flooded  artificially  at  certain  seasons.  Far  the 
greatest  amount  of  the  rice  of  the  world  is  produced  in 


FIG.  266.— Rice.— 
After  WOSSIDLO.  • 


270 


A  TEXT-BOOK  OF  BOTANY 


India,  China,  Japan,  and  the  East  Indies;  but  our  own  Gulf 
States  are  developing  the  industry  rapidly.  The  Carolina 
rice  is  said  to  be  the  best  in  the  market,  and  before  the 
Civil  War  South  Carolina  was  our  great  rice-producing 
State.  In  1899,  however,  Louisiana  produced  more  than 
twice  as  much  rice  as  all  the  other  Gulf  States  combined, 
South  Carolina  being  second.  Rice  in  the  husk  is  called 
paddy;  and  this  is  the  general  name  also  for  rice  in  India. 
(2)  SUGAR-CANES. — The  ordinary  sugar  of  commerce  is 
cane-sugar,  which  is  obtained  mostly  from  sugar-cane; 

but  in  Europe  it  is  ob- 
tained largely  from  beets. 
Sugar-cane  is  a  tropical 
and  subtropical  grass,  a 
native  of  the  East  In- 
dies, but  is  cultivated 
wherever  there  is  a  warm 
climate,  a  deep  rich  soil, 
and  abundant  moisture. 
The  plant  is  about  the 
height  of  corn,  but  has  a 
much  more  slender  stem, 
and  bears  at  the  summit 
a  very  large  and  spread- 
ing flower  cluster  (Fig. 
267).  Its  cultivation  is 
usually  carried  on  in  large 
plantations,  our  greatest 
sugar-producing  State  be- 
ing Louisiana.  When  the 
canes  (as  the  stems  are 
FIG.  26?.— Sugar-cane.— After  WOSSIDLO.  called)  are  mature,  they 

are  cut,  stripped  of  their 

leaves,   and   crushed.     Associated  with   the  production  of 
sugar  as  by-products  are  the  various  sirups  or  molasses. 


MONOCOTYLEDONS 


271 


In  1903,  the  greatest  sugar-producing  regions  of  the  world 
stood  in  the  following  order:  Cuba,  Java,  Hawaiian  Islands, 
and  Louisiana. 

(3)  LAWN,  PASTURE,  AND  HAY  GRASSES. — This  group 
includes   numerous   grasses   that   have   been   selected   for 
certain  combinations  of  qualities.     For  example,  blue  grass 
is  one  of  the  most  fa-     ^^^^^^^^^^^^^^^^^^^^^^ 

mous     grasses     for     all 

,  ,  vJy  .y*,vv3&a&- 

these  purposes;  red  top 

is  a  prominent  pasture 
grass;  and  timothy  is 
one  of  the  best  hay 
grasses. 

(4)  BAMBOO.  —  In 
tropical  and   subtropic- 
al   countries    the    huge 
grasses  called   bamboos 
are     extremely     useful 
(Fig.  268).      Some  spe- 
cies reach  seventy  to  one 
hundred  feet  in  height 
and  a  foot  in  diameter, 
forming  regular   groves 
and  forests.     Their  very 
hard,   light,  and    tough 
stems  are  put  to  innu- 
merable uses,  including 
house-building,    bridge- 
building,  light  wickerwork,  and  weaving  of  various  kinds. 
The  manufacture  of  fishing-rods  from  split  bamboo  is  well 
known;   but  the  ordinary  fishing-poles  are  stems  of  a  kind 
of  bamboo  that  is  native  to  our  Southern  States,  where  it 
covers  extensive  areas  that  are  called  cane-brakes. 

158.  Palms. — The  Palm  Family  (Palmacece)  is  the  great 
tree  group  of  the  Monocotyledons.     Although  palms  are 


and 


PRANTL. 


A  TEXT-BOOK  OF  BOTANY 


characteristic  tropical  and  subtropical  plants,  they  are  such 
well-known,  beautiful,  and  useful  forms  as  to  deserve  promi- 
nent mention.  The  habit  of  the  body  is  very  familiar, 


FIG.  269.— A  com 


fan-palm. 


being  a  conspicuous  feature  in  every  tropical  landscape. 
The  usually  tall,  unbranched,  columnar  trunk  bears  at  its 
summit  a  crown  of  huge  leaves,  which  are  of  either  the 
pinnate  or  the  palmate  type.  Besides  these  palms,  there  are 
low  forms  and  branching  forms,  while  the  rattan  palms 


MONOCOTYLEDONS 


273 


have  climbing,  rope-like  stems  that  sometimes  become  hun- 
dreds of  feet  long.  Species  with  palmate  leaves  are  spoken 
of  as  fan-palms,  the  palmetto  of  the  Southern  States  being 
an  illustration  (Fig.  269),  and  also  the  very  interesting 


FIG.  270. — The   Washington   palm  ;   a  fan-palm  of  the  desert  region  of  Southern 
California  and  adjacent  Arizona. — From  World  To-day. 

Washington   palm  of  the  desert  region  of  Southern  Cali- 
fornia and  adjacent  Arizona  (Fig.  270);    the  others  are 


274 


A  TEXT-BOOK  OF  BOTANY 


feather  palms  (Fig.  271).  The  flower  clusters  are  enor- 
mous, each  cluster  enclosed  at  first  in  a  huge  bract,  which 
is  often  hard.  In  usefulness  to  man  no  monocotyle- 

donous  family  exceeds 
the  palms  except  the 
grasses.  Some  of  the 
prominent  species  are 
as  follows: 

The  coconut-palm 
is  the  most  widely 
distributed  palm,  be- 
ing found  in  all  trop- 
ical countries,  and 
never  very  far  from 
the  sea,  except  as 
planted  by  man  (Fig. 
272).  Its  slender 
trunk,  about  two  feet 
in  diameter,  rises  to 
a  height  of  sixty  to 
one  hundred  feet 
and  bears  a  crown 
of  downward  curv- 
ing pinnate  leaves. 
The  coconut  of  com- 
merce is  well  known. 

It  is  really  a  stone-fruit  (§  143),  in  which  the  ovary  wall 
has  ripened  in  two  layers:  the  outer  a  fibrous  husk,  corre- 
sponding to  the  flesh  in  a  peach;  the  inner  a  heavy  bony 
layer.  When  on  sale,  the  outer  husk  has  usually  been 
stripped  off,  and  at  one  end  of  the  bony  coat  three  round 
black  scars  are  seen,  which  indicate  that  the  pistil  is 
made  up  of  three  carpels.  All  parts  of  the  plant  are 
used,  not  only  the  nuts  and  the  oil  from  them,  but  also  the 
leaves,  the  root,  the  sap  of  the  young  parts,  etc. 


FIG.  271.— A  feather  palm,  closely  related  to  the 
date-palm. — After  ENGLER  and    PRANTL. 


MONOCOTYLEDONS 


2Y5 


The  date-palm  finds  its  most  congenial  home  in 
Arabia,  but  is  also  extensively  cultivated  in  northern  Africa 
(Fig.  273).  It  becomes  a  very  large  tree,  thriving  in  a 
hot,  dry  climate  and  sandy  soil;  and  this  makes  it  in- 
valuable in  semitropical  desert  regions.  The  enormous 
yield  of  a  single  tree  is  indicated  by  the  fact  that  it  is  long- 
lived  and  that  it  may  yield  300  to  500  pounds  of  dates 
in  a  single  season.  Great  interest  attaches  to  the  fact 
that  the  date-palm  promises  to  become  commercially  im- 
portant in  certain  regions  of  California  and  Arizona  that 
seem  otherwise  to  be  hopeless  from  an  agricultural  point  of 


FIG.  272. — Coconut-palms  in  a  Filipino  village. — Photograph  by  RITCHIE. 

view,  since  it  thrives  in  any  amount  of  heat  and  drought, 
and  can  endure  more  alkali  in  the  soil  than  any  other 
profitable  plant.  This  is  the  palm  of  the  Bible  and  of 
ancient  writings  in  general.  Its  habit  is  shown  in 
Fig.  271. 


276 


A   TEXT-BOOK  OF  BOTANY 


The  sago-palm  is  a  native  of  the  East  Indies,  and  is 
extensively   cultivated   there.     It   has   an   extraordinarily 


FIG.  273. — Base  of  a  date-palm,  showing  two    fruit  clusters  and   the  trunk 
ensheathed  by  old  leaf  bases. 


MONOCOTYLEDONS 


277 


large  pith,  which  is  filled  with  starch;  and  sometimes,  it 
is  said,  as  much  as  700  pounds  of  pith  are  obtained  from 
a  single  tree.  This  starch  reaches  Europe  and  America  in 
the  form  of  sago. 

The  list  of  palms  and  of  their  uses  is  a  very  long  one; 
but  the  illustrations  given  will  show  that  the  family  con- 
sists of  forms  used  for  the  greatest  variety  of  purposes  by 
millions  of  people. 

159.  Lilies. — In  the  structure  of  its  flowers  the  Lily 
Family  (Liliacece)  may  be  regarded  as  the  typical  family 
of  Monocotyledons.  With  three  as  the  definite  flower 
number,  with  ;i 
brightly  colored 
and  often  con- 
spicuous .  corolla 
or  perianth,  and 
with  the  ovary 
superior  (§  138), 
there  is  no  rea- 
son why  most  of 
the  members  of 
the  family  should 
not  be  recognized 
easily  (Fig.  274). 
Nearly  all  of 
them  are  terres- 
trial herbs ;  and 
they  are  notably 
forms  with  bulbs,  rootstocks,  etc.,  which  enable  them  to 
put  up  rapidly  at  the  coming  of  a  favorable  season.  The 
family  is  better  known  for  its  beauty  than  for  its  usefulness. 
Among  the  well-known  wild  and  cultivated  forms  are  tril- 
liums,  lily-of-the-valley ,  numerous  true  lilies,  tulips,  dog-tooth 
violet  (Fig.  219),  star  of  Bethlehem,  and  hyacinth;  while 
asparagus  and  onion  are  the  most  common  useful  forms. 


FIG.  274.— The  white  or  Ma- 
donna lily:  A,  flower- 
cluster  ;  B,  flower. — Af- 
ter BAILLO.N. 


278  A   TEXT-BOOK  OF  BOTANY 

The  families  most  likely  to  be  confused  with  the  lilies 
are  the  Amaryllis  Family  (Amaryllidacece)  and  the  Iris 
Family  (Iridacece),  but  in  both  of  these  the  ovary  is  inferior 
(§  138)  and  appears  beneath  the  flower.  Among  the 
amaryllis  forms  (those  with  six  stamens)  are  narcissus 
(including  daffodils  and  jonquils),  snowdrop,  snowflake 
(Fig.  220),  tuberose,  and  certain  so-called  lilies.  Among 
the  iris  forms  (those  with  three  stamens)  are  iris  (including 
the  various  flags)  (Fig.  242),  crocus,  and  gladiolus. 

160.  Orchids. — In  number  of  species  the  Orchid  Family 
(Orchidacece)  is  the  greatest  family  of  the  Monocotyledons; 
but  orchids  are  comparatively  rare  plants,  not  extensively 
distributed,  and  often  very  much  restricted.     In  actual 
number  of  individual  plants  they  are  not  to  be  compared 
with  the  grasses,  or  even  with  the  lilies.     They  are  noted 
for  their  remarkably  irregular  flowers,  whose  bizarre  forms 
and  brilliant  coloration  are  associated  with  insect  visits. 
In  fact,  the  orchids  may  be  said  to  have  specialized  in 
adaptations  to  insects  (§  147).     They  can  always  be  recog- 
nized among  Monocotyledons  by  their  inferior  ovary  and 
by  the  remarkable  modification  of  one  of  the  petals  (appar- 
ently the  lowest  one),  which  always  differs  from  the  others 
in  size  and  form,  and  is  called  the  lip.     Sometimes  the  lip 
is  like  an  inflated    pouch  or  sac,   as  in  the  lady-slipper 
(Fig.   275);  and  often  it  develops  a  conspicuous  hollow 
spur  (Fig.  243).     The  great  display  of  the  family  is  in  the 
tropics,  and  there  many  of  them  are  perching  plants  (§  41). 
The  tropical  forms  are  most  prized  as  greenhouse  plants, 
and  a  good  collection  of  orchids  in  bloom  is  exceedingly 
attractive. 

Very  little  use  has  been  made  of  orchids,  the  best  known 
useful  product  being  vanilla,  which  is  extracted  from  the 
fruit  of  a  climbing  orchid  native  in  Mexico. 

161.  Other    useful    Monocotyledons. — Two    useful    and 
well-known  Monocotyledons  do  not  belong  to  any  of  these 


FIQ.  275.— La.  ly-slippers.— After  GIBSON. 
19  279 


280  A  TEXT-BOOK  OF  BOTANY 

great  and  representative  families,  and  they  deserve  to  be 
mentioned  in  this  general  survey. 

The  banana  belongs  to  a  small  family  most  nearly 
related  to  the  orchids;  and,  although  a  tropical  plant,  it  is 
coming  into  common  use  as  a  foliage  plant  on  account  of  its 


FIG.  276. — A  banana  plant. — After  ENGLER  and  PRANTL. 

beautiful  leaves,  associated  with  its  relative  the  canna. 
It  grows  from  ten  to  forty  feet  high,  although  it  is  an  herb, 
and  bears  a  crown  of  very  large,  pinnately  veined  leaves 
(Fig.  276).  From  fifty  to  one  hundred  and  fifty  fruits  are 
produced  in  a  single  cluster,  and  a  plant  bears  only  once. 


MONOCOTYLEDONS  281 

There  are  many  varieties  of  bananas;  but  the  Martinique, 
with  large  yellow  fruit,  is  the  one  most  extensively  culti- 
vated. The  chief  banana-producing  regions  are  the  West 
Indies  and  Central  America;  but  bananas  are  grown  also 
in  Florida,  Louisiana,  and  California. 

The  pineapple  is  developed  by  a  low  plant  producing  a 
tuft  of  stiff,  sword-shaped  leaves,  in  the  center  of  which  a 
single  pineapple  arises  (Fig.  277).  It  is  a  native  of  tropical 


FIG.  277.— A  pineapple  plant. — From  Dictionary  of  Gardening. 

America,  and  our  supply  comes  chiefly  from  the  West 
Indies,  Bahama  Islands,  and  Florida.  The  nature  of  this 
peculiar  fruit  has  been  described  (§  143). 


CHAPTER  XVII 

DICOTYLEDONS:   AECHICHLAMYDE.5J 

162.  The    two    great    divisions    of    Dicotyledons. — The 
Dicotyledons  are  a  much  larger  group  than   the  Mono- 
cotyledons, containing  more  than  200  families  and  about 
100,000  species.     Most  of  them  are  easily  recognized  by  the 
floral  number  five  or  four,  the  net-veined  leaves,  and  the 
arrangement  of  the  vascular  bundles  of  the  stem  in  a  hollow 
cylinder.     There  are  two  great  divisions  of  Dicotyledons: 
the  Archichlamydece ,  whose  sepals  and  petals  are  either  want- 
ing or  entirely  separate;  and  the  Sympetalw,  whose  corollas 
are  sympetalous  (§  133).     This  is  by  no  means  the  only  dif- 
ference, but  it  is  the  one  used  to  form  the  names. 

The  Archichlamydese  comprise  about  three-fourths  of  the 
families  and  three-fifths  of  the  species  of  Dicotyledons,  and 
the  group  is  so  extensive  and  intricate  that  only  a  slight 
acquaintance  with  it  is  possible  at  first.  Five  conspicuous 
families  or  groups  are  selected  on  account  of  their  repre- 
sentative character  and  common  occurrence. 

163.  The  tree  group. — In   the   lower  stretches  of  the 
Archichlamydese  there  are  a  number  of  small  families  that 
include  our  most  common  hardwood  or  deciduous  trees, 
and  this  assemblage  of  conspicuous  forms  may  be  considered 
together,  without  selecting  any  special  family.      They  in- 
clude elms   (Fig.  44),  sycamore,   walnuts,   hickories,   oaks 
(Fig.  43),  chestnuts,  willows,  poplars  (cotton woods),  birches, 
beech,  etc.     These  trees  are  all  characterized  by  their  simple 
and  inconspicuous  flowers,  which  are  usually  monoacious  or 

282 


DICOTYLEDONS:  ARCHICHLAMYDE^E 


283 


dioecious  (§  137)  and  wind-pollinated.  A  very  character- 
istic flower-cluster  occurs  in  many  of  these  forms,  being  a 
spike-like  cluster,  but  having  conspicuous  scales  or  bracts 
subtending  individual  flowers  or  small  groups  of  flowers. 
It  is  called  the 
ament  or  catkin; 
and  familiar  illus- 
trations are  found 
on  willows  (Fig. 
278),  cotton  woods, 
birches,  and  alders 
(Fig.  279).  Both 
staminate  and  pis- 
tillate flowers,  or 
only  one  kind,  may 
be  in  aments. 

In  higher  fami- 
lies with  more  con- 
spicuous and  usual- 
ly insect-pollinated 

flowers,  other  common  trees  occur,  as  the  tulip-tree  (white 

poplar),  magnolia,  lin- 
den, maple,  buckeye, 
box-elder,  locust,  sweet- 
gum,  and  tupelo  (black- 
gum);  and  among  the 
Sympetalse  the  ash  be- 
longs. The  very  names 
of  these  trees  suggest 
the  characteristic  forms 
of  our  great  deciduous 
forest,  which  once  ex- 
tended in  almost  un- 


FIG.  278. 


.1  K 

Catkins  of  willow:   A,  staminate;  £,  pis- 
tillate. 


n 


n 


B 


Fio.  279. — Catkins   of   alder;   ^4,  branch  with 

staminate    (n)    and    pistillate    (m)    catkins;     broken  SW66P    from     the 
B,  pistillate  catkin  in  the  next  year  (when 
the  seeds  are  ripe). — After  WARMING. 


prairies  to  the  Atlantic 


284  A  TEXT-BOOK  OP  BOTANY 

Coast.  The  beauty  and  variety  of  this  forest  is  one  of  the 
distinguishing  characters  of  the  vegetation  of  the  United 
States,  and  its  abuse  is  equally,  characteristic  of  our  early 
history.  This  great  forest  region  of  deciduous  trees  is 
spoken  of  in  general  as  the  Atlantic  forest;  and  in  it  the 
conifers  are  sparingly  represented,  either  mixed  through  it 
or  in  small  patches.  In  the  rich  soils  of  the  central  States, 
as  in  Ohio,  Indiana,  Illinois,  Kentucky,  Tennessee,  and 
Missouri,  the  deciduous  forest  reaches  its  culmination  in 
variety,  vigor,  and  purity. 

Only  one-fourth  of  our  timber  comes  from  these  hard- 
wood trees,  the  other  three-fourths  being  supplied  by  coni- 
fers (§  128);  and  among  them  the  oaks  are  the  most  useful, 
furnishing  more  than  one-half  the  hardwood  timber.  Next 
in  importance,  so  far  as  output  is  concerned,  and  in  the  fol- 
lowing order,  are  tulip-tree  (white  poplar,  furnishing  the 
so-called  poplar  lumber),  maple,  elm,  poplar  (cotton wood), 
linden  (basswood),  sweet-gum  (red-gum),  ash,  chestnut, 
birch,  hickory,  black  walnut,  sycamore,  etc.  In  actual 
market  value  of  the  lumber,  that  is,  the  comparative  value 
of  the  same  amount  of  lumber  of  each  kind,  the  order  is  as 
follows:  black  walnut,  elm,  oak,  ash,  tulip-tree  (white  pop- 
lar), chestnut,  maple,  sweet-gum  (red-gum),  linden  (bass- 
wood),  poplar  (cotton wood),  etc.  Of  course  this  order  of 
output  and  of  value  cannot  be  a  fixed  one,  but  it  serves  to 
indicate  the  situation  at  the  last  census. 

164.  Buttercups. — The  Buttercup  Family  (Ranuncula- 
cece),  usually  called  the  Crowfoot  Family,  represents  very 
well  the  herbs  with  the  simpler  flowers  that  belong  to  the 
Archichlamydeae.  Taking  an  ordinary  early  spring  butter- 
cup as  an  example,  there  are  five  green  sepals,  five  yellow 
petals,  numerous  stamens,  and  a  little  head  of  numerous 
carpels  growing  as  separate  pistils.  This  last  character, 
the  distinct  carpels,  is  quite  an  important  feature;  and 
flowers  that  have  it  are  said  to  be  apocarpous  (Fig.  280). 


DICOTYLEDONS:  ARCHICHLAMYDE^E  285 

It  must  not  be  thought  that  in  this  family  and  its  allies  the 
sepals  and  the  petals  are  always  just  five  in  number;  for 


FIG.  280. — Apocarpous  flower  of  a  buttercup,  showing  the  head  of  distinct  carpels. 
— After  BAILLON. 

they  may  be  more  numerous  and  may  become  even  in- 
definitely   numerous,   as    in    the    water-lily.     Other   well- 


A  B  «C 

FIG.  281. — Flowers  and  pods  of  the  Mustard  Family:  A,  cluster  of  flowers  and 
young  pods;  B,  ripe  pod;  C,  opening  pod  showing  seeds  attached  to  the  false 
partition. — After  WARMING. 


286  A   TEXT-BOOK  OF  BOTANY 

known  representatives  of  the  family  are  clematis,  anemone, 
hepatica,  marsh  marigold,  and  peony  (Fig.  207);  and  also 
the  spurred  larkspurs  and  columbines.  Closely  related  to 
this  family  are  a  number  of  smaller  ones,  that  share  its 
general  characters,  and  that  contain  such  familiar  plants  as 
May-apple,  water-lilies,  barberry,  bloodroot,  poppies,  etc. 

Nearly  related  to  the  buttercups  is  a  peculiar  family, 
containing  several  well-known  plants,  and  known  as  the 
Mustard  Family  (Crucifercc).  The  flowers  are  peculiar  in 
having  four  sepals  in  two  sets,  four  petals  in  one  set, 
six  unequal  stamens  (two  short  and  four  long),  and  one 
carpel  whose  ovary  is  divided  by  a  "false  partition," 
giving  to  the  pod  (long  or  short)  the  appearance  of  being 
made  up  of  two  carpels  (Fig.  281).  Not  only  is  the  family 
to  be  recognized  by  this  singular  floral  structure,  but  also 
by  its  more  or  less  pungent  taste,  which  reaches  an  extreme 
expression  in  commercial  mustard,  which  is  made  by  grind- 
ing to  powder  the  seeds  of  certain  species.  Among  the 
members  of  the  family  that  are  prized  either  for  ornament 
or  for  use  are  stock,  sweet  alyssum,  candytuft,  wallflower, 
watercress,  horseradish,  mustard,  cabbage,  turnip,  radish, 
etc. 

165.  Roses. — This  family  (Rosacece)  is  one  of  the  best- 
known  and  most  useful  families  of  the  temperate  regions. 
Many  of  the  flowers  have  a  structure  that  suggests  that  of 
the  buttercups,  but  the  family  is  so  extremely  varied  in  this 
respect  that  no  general  description  can  include  them  all. 
In  addition  to  such  beautiful  ornamental  forms  as  the  roses, 
the  family  contains  a  remarkable  collection  of  valuable 
fruits.  These  fruits  may  be  considered  under  three  heads: 

(1)  BERRIES.— It  so  happens  that  none  of  these  are 
true  berries,  but  their  real  nature  has  been  explained  (§  143). 

Strawberries  are  so  hardy  that  they  may  be  grown  in 
almost  any  part  of  America,  from  Alaska  to  Florida  (Fig. 
234).  The  common  cultivated  varieties  have  been  derived 


DICOTYLEDONS:  ARCHICHLAMYDE^  287 

from  a  wild  species  native  along  the  Pacific  Coast  of  Amer- 
ica and  introduced  into  cultivation  from  Chili  about  two 
centuries  ago.  The  real  cultivation  of  strawberries  in  the 
United  States,  however,  began  about  sixty  years  ago,  but 
did  not  reach  large  proportions  until  after  the  Civil  War. 
Since  that  time  the  growth  of  the  industry  has  been  mar- 
velous, thousands  of  varieties  having  been  developed  and 
tested.  By  means  of  refrigerator  transportation  straw- 
berries begin  to  come  north,  from  extensive  plantations  in 
the  Gulf  States,  in  February;  and  later,  areas  farther  north 
supply  the  demand  until  46°  north  latitude  is  reached. 

The  plants  propagate  by  runners  (§  23),  which  are  put 
forth  after  blooming  and  strike  root;  and  the  new  plants 
thus  started,  either  transplanted  or  allowed  to  remain,  bear 
t he  next  year.  These  runner-propagated  plants  are  set  out 
either  in  the  spring  or  in  late  summer,  and  are  protected 
through  the  winter  by  spreading  upon  them  straw  (mulch- 
ing). The  very  common  wild  strawberry  does  not  seem  to 
lend  itself  to  improvement. 

Raspberries  are  grown  more  extensively  in  the  north- 
cast  ern  United  States  than  elsewhere  (Fig.  233).  The  or- 
dinary red  and  black  varieties  have  been  derived  from 
native  American  plants,  which  are  more  hardy  than  those 
t  hat  have  been  introduced.  The  red  raspberry  is  especially 
difficult  to  ship,  and  therefore  the  black  raspberry  is  much 
more  valuable  commercially.  A  peculiar  propagating  habit 
of  raspberries  is  taken  advantage  of  in  their  cultivation.  In 
the  wild  forms,  late  in  the  season,  the  tips  of  the  bending 
stems  (canes)  take  root  and  give  rise  to  new  plants;  in  culti- 
vation this  putting  down  of  the  tips  is  done  artificially. 

Blackberries  belong  to  the  same  genus  (Rubus)  as  the 
raspberries,  and  have  only  recently  become  prominent  as 
cultivated  fruits,  although  in  their  wild  state  they  have 
been  known  and  prized  from  the  earliest  times.  Since  the 
finer  cultivated  varieties  have  been  introduced,  blackberry 


288  A  TEXT-BOOK  OP  BOTANY 

culture  has  developed  rapidly  in  importance,  and  is  suited 
to  almost  all  soils. 

(2)  STONE-FRUITS. — These  valuable  fruits  are  usually  re- 
garded as  belonging  to  a  single  genus  (Prunus).  The  pecul- 
iar ripening  of  the  ovary  into  fleshy  and  stony  layers  has 
been  explained  (§  143)  (Fig.  232). 

Peaches  originated  in  China,  where  they  have  been  cul- 
tivated from  remote  times,  and  came  to  Europe  by  way  of 
Persia  (hence  the  name  Prunus  Persica),  and  from  Europe 
to  America.  The  beautiful  flowers  usually  appear  very  early 
in  spring,  and  hence  they  are  always  in  danger  of  late  frosts. 
On  this  account  peach  culture  is  attended  with  great  risk, 
and  only  those  regions  are  favorable  in  which  blooming  is 
likely  to  be  held  back  and  late  frosts  are  rare.  Curiously 
enough,  these  risks  are  greater  in  the  South  than  in  the 
North.  It  follows  that  the  great  commercial  supply  comes 
from  only  a  few  regions.  One  of  these  is  the  Great  Lakes 
region,  the  prominent  areas  being  in  New  York  and  Canada 
along  the  southeastern  part  of  Lake  Ontario,  along  the 
southern  shore  of  Lake  Erie,  and  on  the  eastern  shore  of 
Lake  Michigan  (the  Michigan  "  fruit  belt ") ;  a  second  great 
region  extends  from  the  shores  of  Long  Island  Sound  to  the 
Chesapeake  Bay  region;  a  third  is  northern  Georgia  and 
Alabama;  a  fourth  extends  from  southern  Illinois  across 
Missouri  into  Kansas;  and  a  fifth  is  almost  the  whole  of 
California  that  is  not  mountainous.  Perhaps  the  best- 
known  peach-growing  States  are  Maryland,  Delaware, 
Georgia,  Michigan,  and  California.  In  a  popular  way 
peaches  are  grouped  as  clingstones  and  freestones;  but 
there  are  intermediate  forms,  and  the  same  variety  may 
be  clingstone  one  season  and  freestone  the  next.  Certain 
smooth-skinned  varieties  are  called  nectarines. 

Apricots  are  intermediate  between  peaches  and  plums  > 
resembling  a  smooth  peach  (nectarine)  in  external  appear- 
ance, and  having  the  smooth  stone  of  a  plum.  They  also 


DICOTYLEDONS:  ARCHICHLAMYDE^J  289 

originated  in  China  or  Japan,  and  the  dangers  in  culti- 
vation are  the  same  as  those  of  the  peach.  The  apricot 
has  never  developed  commercial  importance  in  the  eastern 
United  States  except  in  a  few  places,  notably  in  New  York. 
In  California,  however,  it  is  one  of  the  most  important  com- 
mercial fruits  of  the  State,  having  been  introduced  into  it 
by  the  Mission  Fathers. 

Plums  are  of  so  many  kinds  that  they  can  hardly  be 
spoken  of  all  together.  The  numerous  varieties  have  been 
derived  from  at  least  three  species,  one  European,  one 
Japanese,  and  one  native.  The  most  extensively  grown 
and  commercially  important  plums  are  from  the  European 
stock;  and  the  two  great  areas  of  cultivation  are  California, 
and  the  Northeastern  States  north  of  Pennsylvania  and 
west  to  the  Great  Lakes.  In  California  the  prune  industry 
has  been  extensively  developed,  a  prune  being  simply  a 
plum  that  has  dried  sweet  (without  fermentation)  without 
removing  the  stone  (pit). 

Cherries  are  of  several  varieties,  derived  from  two  Euro- 
pean species.  In  general  they  are  classified  as  sour  cher- 
ries, which  are  largely  grown  in  the  eastern  United  States, 
especially  western  New  York,  for  canning;  and  sweet  cher- 
ries, which  are  most  extensively  cultivated  on  the  Pacific 
Coast.  There  are  a  number  of  native  species  in  the  United 
States,  and  among  them  the  black  cherry  furnishes  a  timber 
much  valued  on  account  of  its  beauty  when  polished. 

(3)  POME-FRUITS. — The  peculiar  character  of  this  type 
of  fruit  has  been  explained  (§  143)  (Fig.  235),  and  the  name 
has  been  used  in  that  of  fruit  culture  in  general,  which 
is  called  pomology.  The  following  forms  all  belong  to  the 
genus  Pirus. 

Apples  have  been  cultivated  from  the  most  ancient 
times;  and  the  thousands  of  varieties  have  all  come  from 
two  wild  species  native  to  southwestern  Asia  and  adjacent 
Europe,  one  giving  rise  to  the  common  apples,  the  other 


290 


A  TEXT-BOOK  OF  BOTANY 


to  the  crab-apples.  This  is  the  most  important  fruit  ui 
the  temperate  regions,  and  North  America  is  the  greatest 
apple-growing  region  of  the  world.  For  commercial  pur- 
poses there  must  be  a  combination  of  such  features  as  pro- 


FIG.  282.— The  common  pear:  A,  flower  cluster;   B,  section  of   a  single  flower; 
C,  section  of  a  fruit  (core  indicated  by  dotted  outline). — After  WOSSIDLO. 

ductiveness,  quality,  and  long-keeping;  and  the  best  region 
of  the  country  to  produce  all  these  extends  from  Nova  Scotia 
to  Lake  Michigan.  Other  important  commercial  regions  are 
Virginia,  the  Plains,  Arkansas  and  the  Ozarks,  and  the  foot- 
hills of  the  Pacific  Coast.  Each  year  these  regions  produce 
about  one  hundred  million  barrels  of  apples.  When  first 
introduced  into  this  country,  the  apple  was  prized  chiefly 
for  the  manufacture  of  cider  and  vinegar;  but  it  is  used  now 
more  extensively  than  any  other  fruit  as  a  fresh  and  evapo- 


DICOTYLEDONS:  ARCHICHLAMYDE^E  291 

ruled  fruit.  Apples  are  usually  propagated  by  budding  and 
grafting  (§  24)  the  desired  variety  on  hardy  young  trees. 

Pears  are  chiefly  derived  from  a  single  European  species 
and  were  introduced  into  this  country  by  the  earliest  set- 
tlers (Fig.  282).  Their  most  successful  cultivation  is  in 
the  Northeastern  States  (from  New  England  to  the  Great 
Lakes)  and  on  the  Pacific  Coast.  In  the  central  States 
extensive  pear  culture  is  attended  with  great  risk  on  account 
of  a  dangerous  disease  known  as  pear-blight  or  fire-blight, 
the  leaves  turning  brown  or  black  as  if  scorched.  This 
is  one  of  the  bacterial  diseases  (§  77).  Unlike  most  fruits, 
pears  are  very  much  improved  when  picked  green  and 
ripened  indoors. 

Quinces  are  well  known,  but  have  not  been  developed  in 
variety  or  in  commercial  importance  as  have  apples  and 
pears,  this  probably  being  due  chiefly  to  the  fact  that  they 
cannot  be  eaten  raw.  The  most  important  quince  orchards 
in  the  United  States  are  in  western  New  York. 

166.  Legumes. — This  is  by  far  the  greatest  family  (Legu- 
ininnsii )  of  the  Archichlamydcac,  and  is  chiefly  distinguished 
by  its  very  irregular  (lowers  and  its  pods,  which  are  derived 
from  a  single  carpel  and  become  more  or  less  elongated  and 
sometimes  remarkably  conspicuous  (Fig.  283).  It  is  the 
peculiar  pods  (legumes)  that  have  given  name  to  the  fam- 
ily. The  ordinary  flowers,  represented  by  the  sweet  pea, 
were  thought  to  resemble  a  butterfly,  and  hence  were  said 
to  be,  papilionaceous.  The  upper  petal  (standard)  is  the 
largest,  and  erect  or  spreading;  the  two  lateral  petals  (wings) 
are  oblique  and  descending;  while  the  two  lower  petals  are 
coherent  by  their  lower  edges  and  form  a  projecting  boat- 
shaped  body  (keel},  which  encloses  the  stamens  and  pistil. 
The  relation  of  this  structure  to  pollination  by  insects  has 
been  described  (§  147).  This  family,  in  its  irregular  flowers 
adapted  to  insect-pollination,  holds  the  same  position  among 
Archichlamydese  that f  he  orchids  do  among  Monocotyledons. 


292 


A  TEXT-BOOK  OF  BOTANY 


In  so  vast  a  family  it  will  be  impossible  to  enumerate  all 
the  forms  that  are  well  known  on  account  of  their  common  oc- 
currence or  usefulness,  but  some  of  them  may  be  mentioned. 
The  sweet  pea,  wistaria,  and  lupine  suggest  the  numerous 
herbaceous  forms  with  showy  flowers.  In  this  family  also 


Fio.  283.— A  leguminous  plant:   A,  flowers  and  pods;  B,  petals  separated  to  show 
standard  (a),  wings  (6),  and  keel  petals  (c). — After  WOSSIDLO. 

are  found  the  numerous  sensitive  plants  (§  17)  character- 
istic of  southwestern  arid  regions  (Fig.  284).  Among  the 
trees  the  following  may  be  mentioned:  common  locust, 
prized  for  both  its  showy  flowers  and  its  valuable  timber; 
honey  locust,  beset  with  conspicuous  thorns  (Fig.  60) ;  red- 
bud,  with  numerous  pink  flowers  appearing  upon  the  naked 
branches  in  early  spring;  and  the  singular  coffee-tree. 

Among  the  useful  forms,  the  so-called  forage  plants  are 
important;  that  is,  plants  used  for  pasturage  or  hay,  just  as 
are  the  grasses.  The  most  common  of  these  is  clover,  a 


DICOTYLEDONS:  ARCHICHLAMYDE^ 


293 


genus  (Trifolium)  containing  many  species.  The  most  im- 
portant one  to  the  farmer  is  the  common  red  clover,  afford- 
ing valuable  pasturage  and  clover  hay,  and  also  improving 
the  soil  (§77).  The 
smaller  white  clover 
is  also  a  very  fa- 
miliar plant  associ- 
ated with  grasses 
in  lawns,  pastures, 
etc.;  and  its  flow- 
ers are  especially 
attractive  to  bees. 
Alfalfa  (lucerne)  is 
another  important 
forage  plant  related 
to  the  clovers,  and 
is  especially  valua- 
ble in  the  West 
where  irrigation  is 
employed.  It  is  a 
native  of  western 
Asia,  has  long  been 
cultivated  in  Eu- 
rope, and  was  in- 
troduced into  Cali- 

.  FIG.  284. — A  sensitive  plant,  showing  the  mconspicu- 

fomia       about       the  ous  flowers  with  numerous  stamens,  and  the  sensi- 

middle    Of    the    last  tive  pinnately  compound  leaves. -After  MEYER 

and  ncHtiMANN. 

century.  Since  then 

it  has  become  the  most  extensively  grown  forage  plant  in 
the  arid  regions  of  the  Pacific  and  Rocky  Mountain  States. 
Besides  the  forage  plants,  the  seeds  of  certain  others  are 
very  familiar  as  food.  The  cultivated  peas  are  natives  of 
southern  Europe  and  Asia,  and  have  been  cultivated  for 
many  centuries.  They  are  distinguished  as  garden  peas  and 
field  peas,  the  latter  being  rather  a  forage  plant.  The  two 


294  A   TEXT-BOOK  OF  BOTANY 

types  of  garden  peas  are  those  with  smooth  seeds  and  those 
with  wrinkled  seeds,  the  former  being  earlier  and  hardier 
(hence  most  common  in  the  market),  the  latter  better  in 
quality.  Beans  are  of  many  kinds,  but  the  common  bean  of 
Europe  does  not  succeed  well  in  the  United  States.  Our 
common  garden  and  field  bean  is  the  kidney  bean,  which 
reached  the  United  States  from  South  America  by  way  of 
Europe.  The  lima  bean  is  also  of  South  American  ori- 
gin, and  is  most  extensively  grown  in  California.  Peanuts 
(goobers)  are  curiously  developed  and  very  familiar  pods. 
After  the  flower  has  fallen,  its  stem  bends  downward  and 
pushes  the  young  pod  into  the  sandy  soil,  where  it  matures, 
and  hence  is  sometimes  called  groundnut.  Several  of  our 
native  legumes  also  have  this  curious  habit.  The  peanut 
is  thought  to  be  a  native  of  Brazil,  and  is  now  grown  in 
all  warm  regions  of  the  world.  In  the  United  States  it 
has  become  an  important  commercial  crop  of  the  Southern 
States  since  1866,  being  chiefly  grown  in  Virginia,  North 
Carolina,  Georgia,  and  Tennessee;  the  annual  yield  being 
four  million  bushels. 

167.  Umbellifers.— This  is  the  highest  family  (UmbelUf- 
erce)  of  the  Archichlamydeae,  and  the  name  has  been  sug- 
gested by  the  fact  that  the  small  flowers  are  massed  in 
flat-topped  clusters  called  umbels  (§  139)  (Fig.  224).     The 
family  is  distinguished  also  by  the  fact  that  the  ovaries  are 
inferior  (§   138).     In  general  they  are  perennial  herbs  of 
north   temperate   regions.     Parsnips   and   carrots   are   the 
thick  tap-roots  of  two  of  the  species,   and  celery  is   the 
blanched  leaf-stalks  of  another.     Some  species  are  charac- 
terized by  their  aromatic  foliage  or  fruit,  as  coriander,  fen- 
nel, and  caraway;  and  one  species  yields  the  deadly  hem- 
lock. 

168.  Other  useful  Archichlamydeae. — Many  well-known 
ornamental  plants  do  not  belong  to  the  representative  fam- 
ilies described  above,  as  violets,  pinks,  geraniums,  nastur- 


DICOTYLEDONS:  ARCHICHLAMYDE^E 


295 


tiums,  fuchsias,  etc.;  and  some  very  useful  plants  also 
belong  to  scattered  families.  These  latter  may  be  grouped 
as  follows: 

(1)  FIBERS. — The  fiber  plants  are  numerous,  but  there 
are  three  very  conspicuous  ones  among  the  Archichlamydeae. 

Cotton. — The  cotton  plant  is  by  far  the  most  important 
fiber  plant  grown,  being  cultivated  over  a  greater  area  and 
used  for  a  larger  number 
of  purposes  than  any 
other  fiber  plant  (Fig. 
285).  The  cultivated  va- 
rieties have  originated 
from  several  tropical  spe- 


cies, but  in  the 
States  the  Sea  Island 
cotton  and  the  upland 
cotton  are  grown  almost 
exclusively.  The  genus 
(Gossypium)  belongs  to 
the  Mallow  Family  (Mal- 
vacece),  to  which  the  hol- 
lyhock and  the  hibiscus 
also  belong,  the  most  con- 
spicuous peculiarity  of 

the   flower    being    the    ap-     Fl°-  285.— The    cotton    plant:   A,   flowering 
,     .  branch  ;   B,  fruit  (boll)  bursting ;  C,  seed 

parent  Coalescence  Of  the  uith  fibers  (lint).— After  WOSSIDLO. 

numerous  stamens  into  a 

central  column  (Fig.  214).  The  capsule  (boll)  of  the  cot- 
ton plant  contains  numerous  seeds,  which  are  covered  with 
long  hairs  (lint)  that  are  the  cotton  fibers  (Fig.  285,  C). 
At  maturity  the  bolls  burst,  and  the  lint  protrudes  in  a 
fluffy,  cottony  mass  (Fig.  285,  B).  The  cotton-gin  was  in- 
vented to  separate  the  lint  from  the  seeds,  and  the  revolu- 
tion it  brought  about  in  the  cotton  industry  is  well  known. 

The  Sea  Island  cotton,  with  its  long  and  silky  fibers,  is 
20 


296 


A  TEXT-BOOK  OF  BOTANY 


the  most  valuable  variety,  reaching  its  greatest  perfection 
along  the  coast  region  of  South  Carolina,  Georgia,  and 
Florida.  The  upland  cotton  is  cultivated  over  a  wider  area, 
but  is  by  no  means  of  so  fine  a  grade.  In  1900,  the  greatest 
cotton-growing  States,  in  the  order  of  the  number  of  acres 
under  cultivation,  were  Texas,  Georgia,  Alabama,  Missis- 
sippi, and  South  Carolina.  There  are  valuable  by-products 
from  the  cotton  plant,  the  seeds  yielding  the  well-known 
cotton-seed  oil. 

Flax. — The  fiber  of  flax  forms  linen  thread  and  cloth, 
and  the  extent  of  its  use  is  second  only  to  that  of  cot- 
ton. The  species  used  is  a 
small  annual  (Linum)  native 
about  the  Mediterranean,  and 
cultivated  from  the  very  ear- 
liest times  (Fig.  286).  The 
fibers  are  found  in  the  stems, 
which  are  subjected  to  a  series 
of  processes  for  separating  the 
fibers  from  the  other  parts. 
The  oil  yielded  by  the  seeds 
is  the  well-known  linseed  oil, 
used  in  paints,  varnishes,  etc. 
Russia  is  the  greatest  flax- 
growing  country  in  the  world; 
but  for  excellence  of  fiber  Bel- 
gium excels,  where  it  is  ased 
in  the  manufacture  of  the 
famous  Brussels  lace.  In  the 
United  States  flax  has  been 
long  cultivated  in  many  States 
for  its  oil;  but  only  recently 
has  its  cultivation  for  fiber  at- 
tracted attention,  and  that  chiefly  in  Michigan,  Wisconsin. 
Minnesota,  and  Washington. 


FIG.  286.— The  flax  plant. — After 
BAILLON. 


DICOTYLEDONS:  ARCHICHLAMYDELE 


297 


Hemp. — This  well-known  fiber  comes  from  an  annual 
plant  native  to  southern  Asia,  but  long  cultivated  in 
Europe,  and  also  naturalized  in  the  United  States  (Fig.  287) 


298  A  TEXT-BOOK  OF  BOTANY 

It  is  a  member  of  the  Nettle  Family  (Urticacece).  As  in 
flax,  the  fibers  used  occur  in  the  superficial  region  of  the 
stem,  outside  the  regular  wood  fibers.  The  most  extensive 
cultivation  of  hemp  is  in  European  Russia;  and  it  is 
somewhat  cultivated  in  the  United  States,  especially  in 
Illinois,  Missouri,  and  Kentucky.  The  name  is  applied 
also  to  any  fiber  that  serves  the  same  purposes  as  true 
hemp;  for  example,  Manila  hemp,  which  is  obtained  from 
a  species  of  banana  which  is  native  in  the  Philippine  Islands 
and  extensively  cultivated  there. 

(2)  BERRIES. — The  conspicuous  berries  not  mentioned 
are  the  currants  and  the  gooseberries,  which  are  members  of 
a  small  family  (Saxifragacece)  closely  related  to  the  Rose 
Family.     These  familiar  plants  belong  to  the  same  genus 
(Ribes)   and   are  natives   of  the   cool   temperate  regions. 
Therefore,  their  chief  cultivation  is  in  northern  Europe  and 
in  the  Northern  United  States  and  Canada.     The  ordinary 
varieties  of  white  and  red  currants  are  well  known  and 
well  cultivated  in  this  country,  but  in  no  country  has  the 
gooseberry  been  developed  to  such  size  and  quality  as  in 
England. 

(3)  GRAPES. — Grapes  are  true  berries,  but  they  are  so 
important  as  to  deserve  separate  mention.     The  genus  is 
Vitis;  and  it  gives  name  not  only  to  the  family  (Vitacece), 
but  also  to  the  culture  of  grapes  (viticulture).     The  cultiva- 
tion of  grapes  for  the  manufacture  of  wine  and  raisins  is  as 
old  as  the  history  of  man.     The  varieties  cultivated  in  the 
Old  World  all  belong  to  a  single  species  (Vitis  vinifera), 
which  is  now  extensively  grown  in  all  countries  bordering 
on  the  Mediterranean,  and  north  to  central  Europe.     This 
same  European  vine  was  introduced  on  the  Pacific  slope  by 
the  early  missionaries;  and  now,  excepting  a  few  famous 
regions  in  Europe,  California  leads  in  the  production  of 
wine  and  raisins,  having  the  largest  vineyards  in  the  world. 
In  the  northeastern  States,  however,  native  varieties  have 


DICOTYLEDONS:  ARCHICHLAMYDE^E  299 

been  developed,  more  for  what  are  called  dessert  purposes 
than  for  wine  and  raisins;  and  this  culture  has  reached  its 
highest  perfection  in  New  York,  New  Jersey,  Maryland, 
Virginia,  and  Ohio.  No  cultivated  plant  is  attacked  by 
more  diseases  than  the  grape,  nor  have  any  plant  diseases 
been  more  fully  studied. 

(4)  CITROUS  FRUITS. — These  fruits  all  belong  to  a  sin- 
gle genus  (Citrus),  whose  species  are  shrubs  or  small  trees, 
natives  of  tropical  and  subtropical  Asia  (China-India). 
The  citrous  fruits  are  numerous,  but  the  three  forms  chiefly 
cultivated  in  the  United  States  and  common  in  markets  are 
as  follows: 

Oranges  are  extensively  cultivated  in  the  United  States 
in  central  and  southern  Florida,  the  delta  region  of  the 
Mississippi,  and  California.  All  the  varieties  are  derived 
from  a  single  species  (Citrus  Aurantium),  and  may  be 
grouped  as  bitter  oranges  and  sweet  oranges,  the  latter 
being  the  chief  market  form.  The  very  popular  seedless 
navel  oranges  of  California  were  introduced  in  1870  from 
Brazil  by  the  United  States  Department  of  Agriculture, 
being  a  chance  seedling  variety. 

A  closely  allied  species  (Citrus  nobilis)  produces  the 
varieties  of  mandarin  or  kid-glove  oranges.  True  mandarins 
are  small  and  light  orange  in  color,  and  are  not  so  much 
prized  in  market  as  the  dark  orange  or  reddish  forms  known 
as  tangerines. 

Grape-fruits  are  extensively  cultivated  in  Florida  and 
California,  all  the  varieties,  most  of  which  have  originated 
in  Florida,  coming  from  Citrus  Decumana,  a  native  of  the 
Malayan  and  Polynesian  Islands.  The  original  and  best 
name  for  this  fruit  is  pomelo,  although  it  is  sometimes  called 
shaddock  as  well  as  grape-fruit.  In  reality,  the  pomelo  or 
grape-fruit  is  the  common  round-fruited  form  of  the 
markets,  while  the  shaddock  is  a  very  different  plant  with  a 
pear-shaped  fruit. 


300 


A  TEXT-BOOK  OP  BOTANY 


Lemons  also  are  cultivated  in  Florida  and  California; 
but  they  are  not  so  hardy  as  the  orange,  and  hence  their 
cultivation  is  more  restricted.  The  chief  foreign  sup- 
ply comes  from  Italy,  Spain,  and  Portugal.  The  lemon 
is  a  variety  of  the  citron  (Citrus  medico);  and  another 
variety  is  the  lime,  which  furnishes  the  commercial  lime- 
juice. 

(5)  TEA. — The  tea  plant  is  a  shrub  native  to  sub- 
tropical Asia,  and  its  dried  leaves  are  one  of  the  most  im- 
portant articles  of  com- 
merce (Fig.  288).  It  has 
been  cultivated  in  China 
and  Japan  for  many  cen- 
turies, and  in  the  last  cen- 
tury extensive  plantations 
were  established  also  in 
India,  Java,  and  Ceylon. 
There  are  three  distinct 
pickings  in  a  season; 
some  of  the  young  leaves 
are  picked  in  April  for 
a  fine  quality  of  tea 
(young  hyson)  which  can- 
not stand  shipping  to  a 
distance;  the  ordinary 
picking  for  the  general 
market  begins  in  May; 
and  later  there  is  a  third 
picking,  which  makes  a  low-grade  tea.  Different  qualities 
and  colors  are  produced  by  the  different  treatment  of  the 
same  leaves,  the  numerous  varieties  being  either  green  tea, 
in  which  the  leaves  are  roasted  quickly,  or  black  tea,  in 
which  they  are  dried  slowly  until  they  are  almost  black. 
Outside  of  oriental  nations  the  chief  tea  drinkers  are  the 
Russians,  the  British,  and  the  Dutch. 


FIG.  288.— Flowering  branch  of  the  tea 
plant. — After  BAILLON. 


DICOTYLEDONS:    ARCHICHLAMYDELE  301 

(6)  CHOCOLATE. — Chocolate  is  obtained  from  the  seeds 
of  the  cacao-tree,  a  native  of  Mexico,  which  was  introduced 
into  Europe  by  the  Spaniards,  and  is  now  cultivated  in  all 
tropical  countries.  The  fruit  is  about  the  size  of  a  small 
cucumber  and  contains  numerous  large  flat  seeds  embedded 
in  its  flesh.  The  seeds  are  crushed  to  a  fine  paste,  which  is 
heated  and  run  into  molds.  Coco  is  obtained  from  choco- 
late by  removing  from  it  some  of  its  oil. 


CHAPTER  XVIII 

DICOTYLEDONS:   SYMPETAL-SJ 

169.  General  characters. — The  Sympetalse  include  the 
families  of  highest  rank,  about  fifty  in  number,  among 
which  there  are  many  well-known  plants,   and  some  of 
great  use.    The  representative  families  are  easily  recognized, 
and  five  of  them  will  be  presented,  with  which  a  real  ac- 
quaintance with  the  Sympetalse  may  well  begin. 

170.  Heaths. — In  this  family  (Ericacece)  there  are  often 
ten  stamens,  in  two  sets,  so  that  there  are  five  cycles  of 
floral  parts;  and  thus  such  forms  are  easy  to  distinguish  from 
the   following   families,   in   whose   flowers   there   are   only 
four  cycles.     Heaths  are  usually  woody  plants,  often  shrubs, 
sometimes  trailing,  occasionally  trees.     One  of  the  most 
peculiar  and  constant  features  of  the  family  is  that  the 
anthers  usually  open  at  the  top  and  generally  by  terminal 
pores  (§   134)   (Fig.  213,  B  and  C).     The  species  belong 
chiefly  to  the  cooler  regions,  often  being  the  prominent 
vegetation  in  cold  bogs  and  on  heaths,  to  which  latter  they 
give  name  (Fig.  289). 

Trailing  arbutus,  bearberry  (kinnikinick),  heather,  rho- 
dodendron (Fig.  290),  azalea,  mountain  laurel,  winter- 
green,  and  corpse-plant  (Indian  pipe)  are  familiar  forms; 
while  huckleberries,  blueberries,  and  cranberries  are  staple 
fruits.  The  cranberries  grow  wild  in  mossy  (sphagnum) 
bogs  in  the  cool  temperate  regions  of  both  America  and 
Europe.  Two  kinds  usually  appear  in  market:  the  small 


DICOTYLEDONS:  SYMPETAI^E  303 

cranberry,  obtained  from  wild  plants;  and  the  large  cran- 
berry, extensively  cultivated  in  several  Northern  States, 
especially  in  Massachusetts,  New  Jersey,  and  Wisconsin. 


Fio.  289.— Heath  plants:  A,  Lyonia;  B  and  C,  two  species  of  Catfiope. — After 

DRUDE. 


Huckleberries,  a  market  name  that  includes  blueberries, 
have  not  as  yet  been  cultivated  for  commercial  purposes, 
but  are  picked  from  wild  plants,  large  areas  of  which  are 


304 


A   TEXT-BOOK   OF  BOTANY 


sometimes  protected.     In  Maine,  the  protected  "blueberry 
barrens"  is  said  to  include  an  area  of  about  150,000  acres. 


FIG.  290. — A  flower-cluster  of  rhododendron. — After  HOOKER. 


171.  Nightshades. — This  great  family  (Solanacece)  in- 
cludes plants  with  more  or  less  conspicuous  and  regular 
tubular  corollas.  The  flowers  have  four  cycles,  a  character 
which  distinguishes  this  family  from  the  former  one;  and 
regular  corollas,  a  character  which  distinguishes  it  from  the 
next  one.  Perhaps  the  most  familiar  illustration  of  the 
general  type  of  flower  is  the  morning-glory,  which  belongs  to 


DICOTYLEDONS:  SYMPETAL.E 


305 


a  small   related   family.      A  very  general   feature  of  the 
nightshades  is  their  rank-scented   foliage,  the  leaves  and 


Fio.  291. — Branch  of  thorn-apple  (Nightshade  Family),  showing  flowers  and 
fruit.— After  BA.ILLON. 

fruits  of  some  of  them  being  very  poisonous.  Among 
the  familiar  plants  are  capsicum  (red  pepper),  ground 
cherry,  belladonna,  matri- 
mony vine,  henbane,  petu- 
nia, and  thorn-apple  (jim- 
son-weed)  (Figs.  291  and 
292);  while  the  three  fol- 
lowing are  of  great  com- 
mercial importance: 

Potato. -^This  most  com- 
mon of  all  vegetables  is 
often  called  Irish  potato, 
because  of  its  general  use 
in  Ireland;  but  it  is  a  na- 
tive of  the  mountainous 
region  of  America  from  southern  Colorado  to  Chili.  Like 
corn  (maize),  potatoes  were  found  in  cultivation  by  natives 


FIG.  292.  — Thorn-apple 
(Nightshade  Family) : 
A,  longitudinal  section 
of  flower;  B,  dehiscence 
of  the  fruit  (bur).— Af- 
ter BAILLON. 


306  A  TEXT-BOOK  OF  BOTANY 

upon  the  discovery  of  America,  and  were  introduced  into 
Europe  by  the  Spanish  conquerors,  probably  from  Peru. 
For  nearly  two  centuries,  however,  their  importance  was 
not  appreciated;  but  now  there  are  ten  times  as  many 
bushels  of  potatoes  produced  in  Europe  as  in  the  United 
States,  the  entire  European  crop  being  said  to  aggregate 
more  bushels  than  the  entire  wheat  crop  of  the  world.  New 
York  is  our  great  potato-producing  State.  There  are  hun- 
dreds of  varieties,  new  ones  replacing  old  ones  every  year; 
but  they  are  all  derived  from  a  single  species  (Solanum 
tuberosum).  It  should  be  remembered  that  these  tubers 
are  subterranean  stems  (§  27)  enlarged  as  depositories  of 
starch,  the  stem  structure  being  indicated  superficially 
by  the  eyes  (bracts  with  axillary  buds).  In  planting,  the 
tubers  are  cut  in  pieces,  each  piece  containing  one  or  two 
eyes  and  as  much  of  the  food-supply  as  possible. 

Tomato. — The  tomato  was  once  called  love-apple,  and 
was  thought  to  be  poisonous.  It  is  grown  more  extensively 
in  North  America  than  elsewhere;  and  in  the  United  States 
there  is  no  vegetable  so  extensively  grown  for  canning,  about 
300,000  acres  being  required  to  produce  the  annual  crop. 
The  principal  tomato-growing  States  are  Maryland,  New 
Jersey,  Indiana,  and  California.  The  numerous  kinds  vary 
in  form  and  color,  all  coming  from  a  single  species  (Lyco- 
persicum  esculentum) ,  which  is  native  to  the  Andean  region 
of  South  America. 

Tobacco. — It  is  well-known  that  the  Indians  used  tobacco 
long  before  the  discovery  of  America,  but  never  excessively 
(Fig.  208).  From  America  its  use  was  introduced  into 
Europe,  gradually  extending  to  the  Asiatic  nations,  until 
now  the  Turks  and  Persians  are  the  greatest  smokers  in  the 
world.  In  the  United  States  tobacco  culture  began  in  Vir- 
ginia, at  the  first  settlement  of  the  colony;  and  it  became 
the  leading  industry  also  of  Maryland,  North  Carolina, 
South  Carolina,  Georgia,  and  Kentucky  at  their  first  settle- 


DICOTYLEDONS:  SYMPETALJ5 


307 


ment.  To-day  Florida,  Connecticut,  Pennsylvania,  and 
Wisconsin  lead  in  the  production  of  the  finer  grades;  while 
the  States  producing  the  other  grades  are,  in  their  order, 
Kentucky,  Virginia,  North  Carolina,  Maryland,  Ohio,  In- 
diana, and  Missouri.  The  finest  tobacco  in  the  world  is 
grown  in  Cuba,  that  from  Florida  ranking  second;  while  the 
tobacco  of  Borneo,  Ceylon,  and  the  Philippine  Islands  is 
not  much  inferior.  The  growing  plant  is  handsome,  with 
showy  flowers,  and  is  often  used  as  an  ornamental  plant. 
The  single  species  is  Nicotiana  Ta- 
bacum,  and  is  of  South  American 
origin. 

172.  Labiates.— This  family  (La- 
biatcp")  has  received    its   name   from 
its    two-lipped   or    bilabiate    corolla 
(§  133).     This   does  not  mean  that 
all  plants  with  bilabiate  flowers  be- 
long to  this  family;  but  if  this  char- 
acter is  associated  with  square  stems 
and  opposite  leaves,  and   also   with 
an  ovary  so    deeply    lobed    that    it 
looks  like  four  little  nutlets  in   the 
bottom  of  the  flower,  the  plant  can 

be  regarded  as  a  member  of  the  f am-    FIG.  293.-Catnip  (Mint  Fam- 

•i        /TT        <-»/~vo\          mi         e    ^•  •  Hy)'-  A ,  flower-cluster;  B, 

ily  (Fig.  293).  The  foliage  is  usu-  Bingie  flower.  c?  pistilt 
ally  aromatic,  and  the  family  is  com-  showing  the  deeply  four- 

lobed  ovary.— After  BAJX- 

monly  called  the  Mint  Family.    Many        LON. 
common  wild  plants  and  garden  herbs 

will  be  recognized  as  belonging  here,  familiar  names  being 
sweet  basil,  pennyroyal,  lavender,  mint,  hoarhound,  hys- 
sop, savory,  marjoram,  thyme,  balm,  sage,  rosemary,  cat- 
nip (Fig.  293),  etc. 

173.  Madders. — This  very  large  tropical  family  (Rubia- 
cece)  is  represented  in  our  flora  by  only  a  few  forms,  such 
as  bluets,  buttonbush,  partridgeberry,  etc.,  which  may  be 


308 


A  TEXT-BOOK  OF  BOTANY 


recognized  generally  by  the  regular  tubular  corolla,  the 
inferior  ovary,  and  the  floral  number  four.  However,  the 
tropical  members  of  the  family  yield  two  important  products 
that  should  not  escape  mention. 

C^fee. — The  coffee  plant  (Coffea  arabica)  is  a  native 
of  Arabia  and  Abyssinia,  and  is  a  slender  tree  becoming 
fifteen  to  twenty-five  feet  high  (Fig.  294),  but  rarely  allowed 
to  become  more  than  half  that  height  in  cultivation.  The 

fruit  is  a  dark  scarlet  berry  (Fig. 
295)  containing  two  horn-like 
seeds,  which  are  ordinarily  called 
coffee-beans  (Fig.  296).  The  use 


FIG.  294.— The  coffee-tree. 
After  BAILLON. 


FIG.  295.— Fruiting  branch  of  coffee. 
After  BAILLON. 


of  coffee  can  be  traced  back  in  Arabia  for  only  about  five 
hundred  years,  and  its  use  in  Europe  extends  over  only 
half  that  time.  Coffee  plantations  have  been  established 
in  regions  of  high  annual  temperature  (ranging  from  60° 
to  90°),  Brazil  producing  more  coffee  than  all  other  coun- 


DICOTYLEDONS:  SYMPETAI^E 


309 


tries  combined.  Other 
prominent  coffee-grow- 
ing countries  are  Mexi- 
co, Central  America, 
Java,  Sumatra,  India, 
Ceylon,  Arabia,  Ha- 
waiian Islands,  and  the 
West  Indies.  Of  the 
many  thousand  tons 
shipped  from  these 
countries,  the  United 
States  consumes  nearly 
one-half,  averaging  over 
nine  pounds  a  year  for 
each  inhabitant.  Mocha 


Flo.  297. — Flowering  branch  of  a  cinchona 
plant. — After  BAILLON. 


FIG.  296.— Coffee-plant :  A ,  flowering  branch ; 
B,  berry  ;  C,  section  of  berry  ;  D,  seeds 
(coffee-beans). — After  WOSSIDLO. 


coffee  comes  from  Ara- 
bia, while  the  sources 
of  the  other  kinds  are 
usually  indicated  by  the 
names. 

Cinchona.  —  This  is 
the  name  of  a  genus 
containing  numerous 
species  of  trees  that 
grow  in  South  America, 
chiefly  along  the  east- 
ern slopes  of  the  west- 
ern mountains  (Fig. 
297).  The  bark  yields 
the  well-known  quinine, 


310  A   TEXT-BOOK  OP  BOTANY 

as  well  as  other  alkaloids,  and  is  commonly  called  Peru- 
vian bark.  It  is  stripped  from  the  trees  by  the  Indians 
and  carefully  dried.  Although  the  trees  are  becoming 
more  scarce  every  year,  no  attempt  has  been  made  to 
cultivate  them  where  they  are  native;  but  in  Java,  British 
India,  Ceylon,  Japan,  and  Jamaica  there  are  extensive  plan- 
tations of  cinchona. 

174.  Composites. — This  is  the  highest  family  (Compos- 
ite) of  Dicotyledons,  and  contains  the  most  numerous 
species.  Composites  are  found  everywhere,  but  are  most 
numerous  in  temperate  regions,  where  they  are  usually 
herbs. 

The  name  of  the  family  suggests  the  most  conspicuous 
feature;  namely,  the  organization  of  the  numerous  small 
flowers  into  a  compact  head  which  resembles  a  single  flower, 
formerly  called  a  compound  flower.  So  common  are  the 
Composites  that  the  general  structure  of  the  head  should 
be  understood.  Taking  the  head  of  Arnica  as  a  type  (Fig. 
298,  A),  the  outermost  set  of  organs  consists  of  more  or  less 
leaf-like  bracts  or  scales  (involucre),  which  resemble  sepals 
(not  seen  in  figure) ;  within  these  there  is  a  circle  of  flowers 
with  conspicuous  yellow  corollas  (rays),  which  are  split 
above  the  tubular  base  and  flattened  into  a  strap-shaped 
body  (Fig.  298,  B),  and  much  resembling  petals;  within  the 
ray-flowers  is  the  broad  expanse  called  the  disk,  which  is 
closely  packed  with  very  numerous  small  tubular  flowers 
known  as  disk-flowers.  If  a  disk-flower  be  removed,  it  will 
be  discovered  that  the  ovary  is  inferior,  and  that  arising 
from  it,  around  the  tubular  corolla,  there  is  a  tuft  of  delicate 
hairs  (pappus)  which  represent  the  sepals  (Fig.  298,  C). 
This  pappus  surmounting  the  akene  (§  143)  in  Composites 
may  be  lacking;  it  may  be  a  tuft  of  hairs,  as  in  Arnica, 
thistle,  and  dandelion;  it  may  be  a  cup  or  a  set  of  scales; 
or  it  may  develop  grappling  appendages,  as  in  Spanish 
needles  (Fig.  257)  and  beggar-ticks  (Fig.  258).  Most  of  the 


DICOTYLEDONS:  SYMPETALuE 


311 


heads  of  composites  have  the  general  structure  described 
for  Arnica;  but  in  the  dandelion  and  its  allies  the  disk- 


B 


FIG.  298. — Arnica:  A,  plant  bearing  an  open  head,  showing  the  conspicuous  rays 
and  disk;  B,  ray-flower;  C,  disk-flower. — After  HOFFMAN. 

flowers  are  like  the  ray-flowers,  with  conspicuous  strap- 
shaped  corollas  (Fig.  299). 
21 


312 


A   TEXT-BOOK  OF   BOTANY 


Some  of  the  well-known  forms,  either  wild  or  in  culti- 
vation, are  ironweed,  ageratum,  blazing  star,  goldenrod, 
daisy,  aster,  everlasting,  rosin  weed  (compass  plant),  rag- 


A  D 

FIG.  299. — Dandelion:  A,  two  flower-stalks,  one  head  being  closed  and  showing 
the  double  involucre,  the  other  open  and  showing  all  the  corollas  strap-shaped, 
B,  single  flower;  C,  akene;  D,  receptacle,  with  single  pappus-bearing  akene. — 
After  STRASBURGER. 

weed,  cockle-bur,  zinnia,  sunflower,  dahlia,  cosmos,  mari- 
gold, chrysanthemum,  tansy,  sage-brush,  burdock,  thistle, 
and  dandelion.  The  only  plant  extensively  used  for  food 
is  lettuce. 

175.  Other  useful  Sympetalae. — Some  well-known  plants 
that  are  not  included  in  the  families  given  above,  but  that 


DICOTYLEDONS:  SYMPETAL^ 


313 


should  be  recognized  as  Sympetalae,  are  honeysuckle,  elder, 
lobelia,  bluebell,  primrose,  morning-glory,  lilac,  milkweed, 
gentian,  phlox,  mullein,  snapdragon,  and  verbena.  Some 
additional  prominently  useful  plants  are  as  follows: 

Sweet  potato  belongs  to  the  same  genus  (Ipomoea)  as  the 
morning-glory,  having  long  trailing  stems  and  clusters  of 
the  well-known  large  oblong  or  elongated  roots.  It  is  not 
known  whether  it  is  native  to  the  East  Indies  or  America, 
but  it  is  extensively  cultivated  in  all  warm  countries.  In 
the  United  States  the  cultivation  of  the  sweet  potato  as  a 
commercial  crop  is  confined  almost  exclusively  to  the  South- 
ern States,  but  important  areas  are  found  also  in  New  Jer- 
sey, Ohio,  Indiana,  and 
Illinois.  The  varieties 
called  yams  in  the  South 
are  all  sweet  potatoes, 
and  the  name  really  be- 
longs to  a  very  different 
plant. 

Olive. — The  olive-tree 
has  been  known  and  cul- 
tivated from  the  most 
ancient  times,  and  has 
entered  largely  into  the 
life  and  customs  of  Med- 
iterranean peoples  (Fig. 
300).  It  is  thought  to 
be  a  native  of  southern 
Europe  and  Asia  Minor, 
and  thrives  best  in  dry 
climates  such  as  those  of 

0  1      .  .  T,     .  FIG.  300. — Flowering  branch  of  olive. 

Syria  and  Assyria.     It  is  After  BAILLON. 

cultivated     also     at     the 

Cape  of  Good  Hope,  in  Australia,  and  in  California.  It 
is  a  very  long-lived  tree,  a  thousand  years  having  been 


314  A  TEXT-BOOK  OF  BOTANY 

reported  for  some  individuals.  The  oil  obtained  from  the 
fruit  is  in  as  common  use  in  Mediterranean  countries  as 
butter  and  lard  in  the  United  States.  The  products 
that  reach  this  country  are  olive-oil  and  pickled  olives; 
but  dried  olives  also  are  much  used  in  certain  olive-grow- 
ing regions. 

GOURD  FRUITS. — The  tropical  and  subtropical  family 
(Cucurbitacece)  that  is  popularly  called  the  Gourd  Family 
contains  numerous  forms  that  are  used  by  tropical  peoples 
not  only  as  food,  but  also  in  the  manufacture  of  various 
utensils.  The  fruit  is  characterized  by  its  very  large  size 
and  hard  rind,  and  the  flesh  within  is  often  edible.  The 
best-known  edible  forms  in  the  United  States  are  as  fol- 
lows: 

Watermelon  is  a  native  of  tropical  Africa,  and  has  been 
cultivated  from  the  most  ancient  times.  There  is  no  coun- 
try where  watermelon  culture  is  conducted  on  so  extensive 
a  scale  as  in  the  United  States.  The  chief  commercial  sup- 
ply comes  from  the  Southern  States,  the  so-called  Georgia 
watermelon  being  the  best-known  variety;  but  a  very  large 
melon  industry  has  been  developed  also  in  Colorado. 

Muskmelons  all  belong  to  a  single  species  (Cucumis 
Melo),  which  is  native  to  the  warmer  parts  of  Asia,  but  is 
now  cultivated  all  over  the  world.  It  is  said  that  one-half 
of  the  muskmelon  crop  is  grown  in  New  Jersey;  but  in 
the  western  markets  Michigan  and  Colorado  are  very  im- 
portant centers.  The  two  general  types  of  muskmelons 
are  the  furrowed  type,  with  hard  rinds,  known  as  canta- 
loupes; and  the  netted  type,  with  softer  rinds,  known  as 
nutmeg  melons.  Two  important  varieties  of  nutmeg  mel- 
ons have  been  developed  recently:  the  Osage  melon,  from 
southwestern  Michigan;  and  the  Rocky  Ford  melon,  from 
Colorado. 

Cucumbers  belong  to  the  same  genus  as  muskmelons, 
and  are  derived  from  a  species  (Cucumis  sativus)  native  to 


DICOTYLEDONS:  SYMPETALuE  315 

southern  Asia.  They  are  grown  in  all  parts  of  the  United 
States,  and  their  extensive  use  as  pickles,  etc.,  is  well 
known. 

Pumpkins  were  cultivated  by  the  Indians  in  their  fields 
of  maize,  as  they  are  now,  and  are  probably  of  tropical 
American  origin,  although  no  wild  plants  are  known.  Some 
M/unshes  belong  to  the  same  species  (Cucurbita  Pepo),  but 
others  are  of  Asiatic  origin. 


CHAPTER  XIX 

PLANT  BREEDING 

176.  Definition. — The   purpose   of  plant-breeding  is  to 
improve  cultivated  plants,  just  as  the  purpose  of  animal- 
breeding  is  to  improve  domesticated  animals.     Great  pro- 
gress has  been  made  in  the  science  of  plant-breeding,  so 
that  it  is  possible  now  in  many  cases  to  breed  for  certain 
desired  improvements  with  great  confidence  that  they  will 
be  secured.     The  skilful  plant-breeder  not  only  must  know 
how  to  make  plants  grow,  but  he  must  know  also  the  laws 
connected  with  the  reproduction  of  plants. 

177.  Variation. — The  fact  with  which  the  plant-breeder 
starts  is  that  plants  tend  to  vary.     If  all  the  seeds  from  one 
parent  plant  are  sown,  the  plants  that  come  from  them 
will  all  resemble  the  parent  in  a  general  way;  this  handing 
down  of  similarities  from  one  generation  to  the  next  is  called 
heredity.     But  while  there  is  this  general  resemblance  to  the 
parent,  there  are  variations,  one  or  more  of  the  new  plants 
perhaps  resembling  the  parent  less  than  the  others  do.     It 
is  this  fact  that  makes  plant-breeding  possible;  and  instead 
of  relying  upon  nature  to  present  to  him  all  the  variations 
he  needs,  the  plant-breeder  by  changing  conditions  increases 
the  tendency  of  plants  to  vary,  and  also  by  crossing  multi- 
plies variations.     The  important  thing  is  to  obtain  as  many 
and  as  wide  variations  as  possible. 

178.  Vegetative  propagation. — If  among  varying  plants 
there  appears  one  that  is  desirable,  it  may  be  possible  to 
propagate  it  vegetatively,  that  is,  without  using  the  seed. 

316 


PLANT-BREEDING  317 

Such  propagation  is  much  more  certain,  for  propagation 
by  seed  introduces  variations.  Some  plants  are  propagated 
naturally  in  ll.is  way,  as  those  with  thickened  underground 
shoots  (rootstocks,  tubers,  bulbs)  or  with  runners  (straw- 
berry, etc.). 

Others  are  propagated  by  artificial  methods.  For  ex- 
ample, cuttings,  often  called  slips,  are  pieces  of  the  plant 
that  are  found  to  be  able  to  grow  when  put  in  the  soil,  as  of 
geraniums,  grape-vines,  etc.  Even  leaves  may  be  used  as 
cuttings,  as  in  the  begonia;  and  cuttings  of  the  potato  tuber 
are  used  in  its  propagation.  Grafts  are  cuttings  inserted  in 
plants  (§  24)  (Fig.  55),  and  it  is  common  for  the  plant  in 
which  a  «jraft  is  inserted  (stock)  to  differ  from  the  plant  that 
is  being  grafted  on  it,  securing  among  other  things  greater 
hardiness  and  a  saving  of  time;  for  example,  it  is  common 
to  graft  pears  on  quince  stock.  Budding  is  a  variety  of 
grafting  in  which  only  buds  from  the  desired  variety  are 
grafted  upon  stocks.  Grafting  and  budding  are  very  com- 
mon in  the  cultivation  of  tree  fruits.  Layering  consists 
in  bending  down  a  stem  to  the  ground  and  covering  it  for  a 
short  distance  with  soil;  when  roots  strike  into  the  soil  from 
a  covered  joint,  the  connection  with  the  parent  plant  is  cut, 
and  a  new  plant  is  thus  obtained  (§  23).  This  process  is 
common  with  such  plants  as  gooseberries,  blackberries,  etc., 
and  resembles  in  a  general  way  the  natural  method  of 
propagation  by  runners. 

179.  Crossing. — The  artificial  production  of  hybrids 
(§  149)  is  used  extensively  to  secure  new  varieties  which 
may  be  desirable.  The  process  consists  in  removing  the 
young  stamens  from  the  flower  to  be  operated  upon;  at  the 
proper  time  placing  upon  the  stigma  pollen  from  the  de- 
sired plant,  and  covering  the  flower  or  flower-cluster  thus 
pollinated  with  a  gauze  or  paper  bag  to  prevent  the  ap- 
proach of  any  other  pollen.  The  seeds  thus  obtained  are 
carefully  collected  and  planted,  and  the  new  plants  observed. 


318  A  TEXT-BOOK  OF  BOTANY 

Among  them  there  may  be  found  one  or  more  with  a  desired 
variation,  or  at  least  the  beginnings  of  it.  These  plants  are 
preserved  and  the  others  destroyed.  Often  many  thousands 
of  young  plants  are  thus  started,  and  most  of  them  de- 
stroyed. 

180.  Selection. — When  a  desired  variation  has  appeared, 
the  work  of  improving  and  establishing  it  must  follow. 
This  is  done  by  means  of  selection,  and  it  involves  great  care 
and  patience.  The  selected  plants  are  carefully  guarded,  no 
foreign  pollen  being  allowed  access  to  their  flowers.  Their 
seeds  are  planted,  and  among  the  new  plants  that  come  up 
those  showing  the  desired  variation  are  preserved  and  the 
others  are  destroyed.  This  selection  goes  on  generation 
after  generation  until  only  the  desired  variety  is  produced. 
It  is  then  said  to  be  established,  and  can  usually  be  de- 
pended upon  to  produce  its  kind. 

Even  after  a  variety  has  thus  been  established,  great 
care  must  be  used  in  selecting  from  the  best  plants  seeds 
for  planting,  or  the  variety  will  "run  down/'  It  is  a  great 
mistake  to  suppose  that  seeds  from  inferior  plants  will  do  just 
as  well  for  sowing  as  seeds  from  the  best  plants.  Farmers 
have  learned  this  in  selecting  their  seed-corn,  seed-wheat, 
etc. ;  and  their  success  depends  upon  their  wise  selection  of 
the  seeds  to  plant.  It  is  important  to  know  that  in  this 
selection  of  seed  the  character  of  the  individual  plant  that 
produces  it  is  the  important  thing.  To  select  for  planting 
the  largest  ears  of  corn  from  a  pile  of  corn  does  not  result  so 
well  as  to  select  in  the  field  the  plants  that  produce  on  the 
average  the  best  ears. 

The  process  of  selection  is  being  applied  also  in  the 
development  of  varieties  that  resist  certain  diseases.  For 
example,  in  a  field  that  has  been  ravaged  by  some  disease 
a  few  plants  may  be  found  that  have  resisted  the  attack 
successfully.  This  means  that  the  variation  in  these  plants 
is  a  very  desirable  disease-resisting  power.  Starting  with 


PLANT-BREEDING  319 

these  plants,  therefore,  selection  may  be  able  to  develop 
a  race  remarkably  free  from  this  particular  disease.  This 
method  of  combating  disease  may  sometimes  prove  more 
effective  than  any  attempt  to  save  the  plants  that  are  sub- 
ject to  it. 

The  story  of  the  development  of  the  best-known  varie- 
ties of  cultivated  plants  is  a  very  interesting  one,  telling 
how  promising  varieties  have  been  discovered,  and  with 
what  wonderful  patience  they  have  been  developed  into 
usefulness.  The  recent  great  increase  in  knowledge  of  the 
principles  of  plant-breeding  has  made  the  development  of 
desirable  varieties  more  definite  and  rapid  than  it  has  ever 
been  before. 


CHAPTER  XX 

FORESTRY 

181.  Definition. — The  term  forestry  is  difficult  to  define, 
for  it  includes  much  more  than  is  usually  supposed.     In 
general,  it  is  the  management  of  forests,  so  that  they  may 
serve  their  purpose;  but  the  purpose  of  a  forest  includes 
many  things.     Forestry  does  not  deal  with  individual  trees, 
but  with  an  assemblage  of  trees;  perhaps  it  would  be  best 
defined  as  the  management  of  woodland.    There  are  two  prom- 
inent aspects  of  forestry.     Forests  furnish  wood  crops,  as 
wheat-fields  furnish  wheat  crops;  and  from  this  standpoint 
forestry  resembles  agriculture.     But  forests  also  hold  im- 
portant relations  to  climate,  water-supply,  etc.;  and  from 
this  standpoint  they  are  to  be  considered  as  features  of  the 
earth's  surface. 

182.  History  of  forestry. — The   history  of  forestry  in 
every  country  has  been  the  same.     At  the  first  settling 
of  a  country  by  civilized  people,  the  forests  were  looked 
upon  as  impediments  to  agriculture,  and  the  clearing  of 
the  forest  was  a  part  of  pioneer  work.     As  forests  cover 
most  of  the  best  land,  this  pioneer  clearing  was  necessary. 
After  agriculture  became  established,  forests  ceased  to  be 
regarded  as  impediments,  and  came  to  be  prized  as  the  source 
of  timber  supply.     They  were  wastefully  ravaged  for  this 
purpose,  the  best  trees  being  culled  out,  countless  young 
ones  destroyed,  and  fires  completing  the  reckless  waste. 
European  countries  passed  through  this  stage  many  years 
ago,  and  the  United  States  is  just  emerging  from  it.     When 

320 


FORESTRY  321 

this  wasteful  use  of  forests  has  proceeded  so  far  that  the 
disastrous  consequences  are  in  plain  sight,  the  forestry  stage 
begins,  and  the  proper  management  of  forests  is  established. 
In  European  countries  forestry  has  been  long  established 
and  has  become  highly  developed,  especially  in  Germany 
and  France.  In  the  United  States  the  Government  has 
established  a  Bureau  of  Forestry,  and  certain  States  have 
adopted  a  definite  forest  policy. 

183.  Supply  forests. — This  name  has  been  suggested 
for  those  forests  used  primarily  as  a  source  of  wood-supply. 
The  crop  of  wood  differs  from  ordinary  crops  in  that  it  is 
natural  growth  and  needs  a  long  period  to  mature.  The 
problem  is  to  obtain  as  much  wood  from  the  forest  as  pos- 
sible year  after  year,  without  diminishing  its  productive- 
ness; in  other  words,  to  use  it  and  preserve  it  at  the  same 
time.  There  is  a  best  time  for  cutting,  that  is,  harvesting, 
in  the  life  of  each  kind  of  tree,  a  time  determined  by  its  size 
and  the  quality  of  its  wood.  The  forest  habit — the  grow- 
ing of  trees  close  together — secures  the  lofty  symmetrical 
trunk,  with  branches  carried  high,  the  most  favorable  form 
for  use.  Trees  that  are  "ripe"  not  only  can  but  should 
be  removed,  that  the  younger  ones  may  come  to  vigorous 
maturity.  In  this  way  a  continuous  succession  of  suitable 
trees  becomes  ready  for  removal,  and  every  tree  in  the 
forest  is  given  an  opportunity  to  do  its  best.  The  thought- 
less cutting  of  trees  usually  secures  one  good  crop  from  a 
forest;  while  a  forest  managed  by  a  forester  yields  a  suc- 
cession of  good  crops. 

When  the  forester  takes  charge  of  a  forest  that  has  had 
no  management,  he  first  removes  the  undesirable  trees; 
but  the  lumberman  would  remove  the  most  desirable. 
The  forester  knows,  however,  that  in  this  way  the  quality 
of  the  remaining  trees  will  be  improved,  and  in  the  long  run 
he  will  get  a  larger  and  better  crop.  The  cutting  is  so 
arranged  that  the  openings  left  will  give  opportunity  for 


A  TEXT-BOOK  OF  BOTANY 

seedlings  to  develop;  so  that  in  a  forest  properly  managed 
there  are  trees  in  every  stage  of  development,  from  seed- 
lings to  those  ready  to  be  cut.  Such  management  is  being 
adopted  not  only  in  large  forests  that  are  prominent  sources 
of  wood-supply,  but  also  on  individual  farms,  where  the 
wood-lot  is  as  carefully  managed  as  the  grain-field.  De- 
tailed plans  for  such  management  can  now  be  obtained  from 
the  Bureau  of  Forestry  or  from  State  foresters,  so  that 
ignorance  is  no  longer  any  excuse  for  mismanagement. 

184.  Protective  forests. — This  name  has  been  suggested 
for  those  forests  that  are  used  primarily  as  a  soil  cover. 
Such  forests  are  used  also  as  supply  forests,  but  their  chief 
purpose  is  to  cover  the  soil.  Forests  are  great  regulators 
of  water-flow,  retaining  the  water  of  rains  and  letting  it 
pass  gradually  into  the  streams.  When  they  are  removed, 
streams  that  formerly  contained  a  steady  supply  of  water 
are  subject  to  alternations  of  flood  and  extremely  low  water. 
When  forests  are  removed  from  water-sheds  and  the  head- 
waters of  rivers,  this  result  becomes  disastrous.  The  head- 
waters of  prominent  rivers  are  generally  in  mountainous 
regions;  and  the  removal  of  forests  there  results  not  only 
in  flooded  rivers,  but  also  in  slopes  stripped  of  their  soil  and 
deeply  gullied.  In  such  regions,  therefore,  the  forest  both 
regulates  the  water-flow  and  protects  the  soil. 

In  consequence  of  these  facts,  the  Government  has  set 
apart  certain  forest  areas  upon  the  head-waters  of  the  prin- 
cipal rivers  as  forest  reservations.  These  reservations  are 
guarded  from  fire  and  from  ruthless  cutting,  but  are  cut  for 
timber  under  proper  forestry  management.  Especially  are 
such  reservations  imperative  in  the  West  where  irrigation 
is  necessary,  which  must  depend  upon  a  steady  supply  of 
water  from  the  mountains.  On  January  1,  1905,  there  were 
sixty-two  such  reservations  in  various  parts  of  the  West, 
including  over  sixty-three  million  acres.  States  also  have 
established  forest  reservations,  most  prominent  among 


FORESTRY  323 

which  are  New  York  and  Pennsylvania;  while  Michigan, 
.Minnesota,  and  other  States  are  following  their  example. 

185.  Reforestation. — In  many  regions  where  forests 
have  been  removed  completely,  and  on  the  treeless  prairies 
and  plains,  trees  must  be  started  and  a  forest  cover  gradu- 
ally developed.  In  European  countries,  where  many  hill 
slopes  had  been  cleared  of  all  trees  and  the  soil  gullied  and 
washed  away,  reforestation  has  been  conducted  on  a  large 
scale.  Many  a  hilly  Oriental  country,  now  barren,  was  once 
forest-clad  and  fertile,  as  Palestine,  whose  streams  have 
disappeared,  and  Mesopotamia,  once  a  garden  watered  by 
the  Euphrates,  but  now  a  desert. 

In  the  United  States  extensive  reforestation  is  required 
only  on  the  prairies  and  plains,  where  active  measures  are 
taken  to  stimulate  tree-planting;  and  perhaps  eventually 
some  real  forests  may  be  developed  in  these  treeless  regions. 
It  may  be  well  to  call  attention  to  the  fact  that  tree-plant- 
ing, such  as  "Arbor  Day  "stimulates,  is  not  forestry;  and 
that  the  real  problem  of  forestry  in  the  United  States  to- 
day is  the  proper  management  of  existing  forests. 


CHAPTER  XXI 

PLANT   ASSOCIATIONS 

186.  Definition. — The  earth's  surface  presents  such  di- 
verse conditions  for  plant  life  that  plants  become  grouped 
according   to   the   conditions  favorable   for  their  growth. 
These  groups  of  plants,  living  together  in  similar  condi- 
tions, are  called  plant  associations,  or  sometimes  plant  so- 
cieties or  plant  communities.     For  example,  a  meadow  is  a 
plant  association  growing  in  conditions  that  favor  certain 
grasses;  a  forest  is  an  association  growing  where  certain 
trees  are  favored,  etc.      In  these  associations  grasses  and 
trees  are  simply  the  conspicuous  types;  but  numerous  other 
plants,  which  the  same  conditions  favor,  are  associated  with 
them.    Each  plant  association,  therefore,  indicates  a  special 
set  of  conditions  for  plant  growth,  and  to  discover  these 
conditions  is  a  very  important  kind  of  field  work. 

187.  Water. — Water  is  probably  the  most  important  con- 
dition that  determines  plant  associations.      The  available 
amount  of  water  for  plants  varies  in  different  areas,  from 
the  very  small  supply  in  deserts  to  the  abundant  supply  in 
swamps  and  lakes.      The  character  of  the  soil  has  a  very 
important  effect  upon  water-supply;  for  some  soils  retain 
water  and  others  do  not,  so  that  what  is  called  the  water- 
level  is  of  varying  depths  (§  39).     Not  only  are  the  amount 
of  water  and  the  depth  of  the  water-level  important,  but 
also  the  substances  that  the  water  contains  in  solution, 
which  may  prevent  certain  plants  from  growing  and  permit 
others. 

334 


PLANT  ASSOCIATIONS  325 

In  any  given  area  the  amount  of  available  water  may 
not  remain  the  same.  For  example,  the  margins  of  ponds 
may  slowly  encroach  upon  the  open  water;  ponds  may  be- 
become  converted  into  bogs;  and  bogs  into  dry  ground.  In 
his  drainage  operations  and  removal  of  forests  man  has  made 
changes  in  the  water-supply  over  extensive  areas.  All  of 
these  changes  involve  the  destruction  of  old  plant  associa- 
tions and  the  coming  in  of  new  ones. 

188.  Temperature. — The  temperature  of  the  air  and  of 
the  soil  during  the  growing  season  is  very  important  in 
determining  the  presence  of  different  plants  upon  any  area. 
For  each  kind  of  plant  there  is  what  may  be  called  a  zero 
temperature,  below  which  it  is  not  in  the  habit  of  work- 
ing. The  succession  of  plants  during  a  single  growing  sea- 
son illustrates  the  distribution  of  plants  by  temperature, 
spring  plants  being  able  to  endure  greater  cold  than  can 
those  of  the  summer.  This  distribution  in  time  indicates 
the  more  important  distribution  in  space  that  is  brought 
about  by  differences  in  temperature. 

Permanent  changes  in  the  temperature  of  a  region,  af- 
fecting the  distribution  of  plant  associations,  are  evident 
only  in  tracing  the  history  of  plants  back  into  what  are 
called  geological  times.  At  certain  times  arctic  conditions 
prevailed  in  regions  now  temperate,  and  this  had  an  im- 
mense influence  on  plant  life. 

Plant  associations  are  not  determined  by  one  condition, 
but  by  a  combination  of  conditions.  The  simplest  illustra- 
tion of  this  fact  may  be  obtained  by  combining  the  water 
and  the  temperature  conditions.  For  example,  if  there  is  a 
combination  of  scanty  water  with  high  temperature,  a  de- 
sert is  the  result;  but  if  the  combination  is  abundant  water 
and  high  temperature,  luxuriant  vegetation  is  the  result. 
Since  the  possible  combinations  of  water-supply,  tempera- 
ture, and  other  conditions  are  endless,  it  is  evident  that 
there  are  very  numerous  plant  associations. 


326  A  TEXT-BOOK  OF  BOTANY 

189.  Light. — All   green   plants   cannot   have   an   equal 
amount  of  light,  and  some  have  learned  to  live  with  a  less 
amount  than  others.     In  a  general  way  this  difference  is 
recognized  in  the  terms  light-plants  and  shade-plants,  and 
it  permits  plants  to  grow  in  strata.     For  example,  in  a 
forest  association  the  tall  trees  form  the  highest  stratum; 
below  this  there  may  be  a  stratum  of  shrubs,  then  tall 
herbs,  then  low  herbs,  then  mosses  and  lichens  growing 
close  to  the  ground.     If  a  forest  is  cleared,  the  remaining 
plants  of  the  association  are  very  much  affected;  and  if  a 
forest  encroaches  upon  another  association  it  is  sooner  or 
later  destroyed.       The  development  of  the  vernal   habit 
in  connection  with  deciduous  forests,  which  was  described 
in  §  27,  is  a  means  by  which  certain  plants  avoid  the  forest 
shade  and  secure  the  forest  soil. 

190.  Wind. — In    regions   of   strong   and   more   or   less 
continuous  wind,  as  near  the  seacoast,  around  the  Great 
Lakes,  and  on  the  prairies  and  plains,  this  condition  has 
much  effect  upon  the  character  of  the  plants.     Wind  is  a 
great  drying  agent,  and  increases  the  loss  of  water  from 
plants  by  transpiration  (§  15),  so  that  plants  exposed  to  it 
must  be  able  to  check  transpiration. 

191.  The  great  groups  of  associations. — For  convenience, 
the  very  numerous  plant  associations  are  grouped  on  the 
basis  of  their  water-supply.     Such  a  classification  is  not  a 
natural  one,  for  no  single  condition  determines  an  asso- 
ciation; but  for  general  purposes  it  serves  well  to  introduce 
the  associations  to  observation.     On  this  basis  there  are 
three  great  groups  of  associations,  as  follows: 

(1)  Hydrophytes. — The    name    means    "water-plants," 
and  applies  to  those  associations  with  an  abundant  water- 
supply,  growing  in  water  or  in  very  wet  soil. 

(2)  Xerophytes. — The  name  means   "drought  plants," 
and  applies  to  those  associations  with  a  scanty  water-sup- 
ply.    True  xerophytes  are  exposed  to  dry  soil  and  air. 


PLANT  ASSOCIATIONS  327 

(3)  Mesophytes.—}fr\\\'wi\  the  two  extremes  of  the  wa- 
ter-supply there  is  a  -n-at  middle  region  of  medium  water- 
supply,  and  plants  of  these  medium  conditions  are  meso- 
phyn-s  ("medium  plants").  It  is  evident  that  mesophytes 
pass  irra<lually  into  hydrophytes  on  the  one  side  and  into 
xerophytes  on  the  other. 


CHAPTER  XXII 

HYDROPHYTES 

192.  Adaptations. — When  a  plant  lives  entirely  or  par- 
tially submerged   in  water,  its  structure  differs  in   many 
ways  from  that  of  an  ordinary  land  plant,  and  these  ad- 
justments to  water  life  are  called  adaptations.     On  parts 
under  water  the  epidermis  is  thin  and  permits  absorption, 
so  that  in  a  completely  submerged  plant  its  whole  surface 
absorbs.     When  this  is  the  case,  the  root-system  is  much 
reduced  in  extent  as  compared  with  a  land-plant  of  the 
same  size,  for  it  is  not  the  only  organ  for  water  absorption. 
In  submerged  plants  the  rigid  tissues  are  less  developed 
than  in  land  plants,  for  the  "buoyant  power  of  water  helps 
to  support  the  plant.     This  fact  may  be  illustrated  by  taking 
from  the  water  submerged  plants  that  seem  to  be  upright, 
with  all  their  parts  spread  out;  upon  removal  they  collapse, 
not  being  able  to  support   themselves.     Water-plants  are 
also  usually  provided  with  air-chambers  and  passageways 
that  the  air  may  be  free  to  reach  the  working  cells. 

A  few  of  the  most  characteristic  hydrophytic  associa- 
tions are  given  as  illustrations,  some  of  which  occur  in 
almost  every  neighborhood. 

193.  Pond  weed    associations. — Water-lilies   and    pond- 
weeds  are  conspicuous  members  of  these  associations,  the 
former  with  floating  leaves   (pads)    (Fig.  301),  the  latter 
often  entirely  submerged.     Associated  with  them  are  nu- 
merous  other   forms  with    floating  or  submerged  leaves. 
The  plants  are  anchored  by  their  roots  and  rootstocks  in 

328 


329 


HYDROPHYTES  331 

the  mucky  bottom;  and  even  when  they  do  not  send  leaves 
up  to  the  surface  of  the  water,  they  usually  send  up  the 
flowers  that  they  may  open  in 
the  air.  In  parks  ;m<l  green- 
houses,  the  great  water-lily  of 
the  Amazon  (Victoria  regia), 
the  largest  of  all  the  water- 
lilies,  is  commonly  seen  (Fig. 
302).  Floating  and  snbmer.nvd 
leaves  are  very  different  in 
form,  and  when  both  kinds 
occur  on  the  same  plant  the 

contrast    is    Striking    (Fig.     303).      1  i<;.     .m<.     Submerge.!     and     aerinl 
1  n  A       T»       A  TV.  leaves  of  a   water    buttercup. — 

194.  Reed    swamps.  —  The        Aftl.rSM«As,,, •„,.,.«. 
reed -swamp     plants    are    tall, 

\\and-like  forms  that  grow  in  the  shallow  margins  of  small 
lakes  and  ponds  (Fig.  304).  Prominent  among  them  are 
cat-tails,  bulrushes,  and  wild  rice;  and  associated  with  these 
tall  forms  the  anowlrat  is  often  found.  This  assemblage 
of  plants  forms  the  usual  high  fringe  along  swampy  shores, 
and  they  have  been  called  the  pioneers  of  land  vegeta- 
tion; for  their  growth  and  the  entangled  detritus  make  the 
water  more  and  more  shallow,  until  finally  the  reed  plants 
are  compelled  to  migrate  into  deeper  water.  In  this  way 
small  lakes  and  ponds  may  become  converted  first  into 
ordinary  swamps,  and  finally  into  wet  meadows.  Instances 
of  nearly  reclaimed  ponds  may  be  found,  where  bulrushes, 
cat-tails,  and  reed  grasses  still  occupy  certain  wet  spots, 
but  are  shut  off  from  further  migration. 

195.  Swamps. — Ordinary  swamps  are  occupied  by  sedges 
and  coarse  grasses,  giving  them  a  meadow-like  appearance. 
Such  swamps  often  border  reed  swamps  on  the  land  side, 
and  encroach  upon  them  as  the  reed  plants  build  up  land. 
With  the  sedges  and  grasses  numerous  other  swamp-loving 
plants  are  found. 


332 


A  TEXT-BOOK  OF  BOTANY 


196.  Swamp    thickets. — A    growth    of    shrubs    or    low 
trees  may  invade  the  sedgy  swamp,  giving  rise  to  a  thicket. 


FIG.  304. — A  reed  swamp. — After  KERNER. 


These  shrubs  and  trees  are  of  very  uniform  type,  being 
mainly  willows,  alders,  birches,  etc. 

This  series  of  associations,  from  pondweed  associations 


334 


336  A  TEXT-BOOK  OP  BOTANY 

to  swamp  thickets,  is  a  very  natural  one,  each  one  often 
passing  gradually  into  the  next. 

197.  Peat-bogs. — This    is    a  peculiar  kind  of  swamp 
association,  characterized  by  the  abundant  growth  of  the 
bog-  or  peat-moss,  and  developed  in  undrained  swamps. 
Growing  out  of  the  springy  moss  turf  there  are  numerous 
peculiar  plants,  such  as  heaths  (Fig.  305)  and  orchids,  and 
the  curious  carnivorous  plants  (§  20). 

198.  Swamp  forests. — Often  trees  encroach  upon  peat- 
bogs, and  a  swamp  forest  is  the  result.     The  chief  types  in 
this  case  are  the  conifers,  and  on  this  bog-moss  foundation 
there  occur  larches,  certain  hemlocks  and  pines,  junipers, 
etc.     The  larch  or  tamarack  is  a  very  common  swamp 
tree  of  the    northern   regions,  usually  occurring  in  small 
patches;  while  the  larger  swamp  forests  are  composed  of 
dense  growths  of  hemlocks,  pines,  etc.  (Fig.  306). 

199.  Salt  marshes  and  meadows. — The  salt  marshes  and 
meadows  near  the   seacoast   are  well  known.      They  lie 
beyond  the  reach  of  ordinary  flood-tide,  but  the  waters  are 
brackish.     In   these  marshes  occur  certain   characteristic 
salt-water  grasses  and  sedges,  giving  the  meadow-like  ap- 
pearance; while  associated  with  them  there  are  numerous 
succulents,  that  is,  fleshy  plants,  characteristic  of  brackish 
water. 

200.  Mangrove  swamps. — This  is  the  most  vigorous  salt- 
water  association.      Mangrove  swamps   occur    along   flat 
tropical  seacoasts  where  the   waters  are  quiet  (Fig.  307). 
The  mangrove  is  a  tree  of  curious  habit,  advancing  slowly 
out  into  the  water  by  means  of  its  prop-roots  and  peculiar 
seeds.     The  seeds  germinate  while  still  upon  the  tree,  so 
that  the  embryos  hang  from  the  trees  and  then  drop  like 
plumb-bobs  into  the  muck  beneath,  where  they  stick  fast 
and  establish  themselves. 


X*- 


CHAPTER  XXIII 

XEROPHYTES 

201.  Adaptations. — The  adaptations  of  plants  to  meet 
drought  are  numerous  and  striking.  The  meager  supply 
of  water  available  for  the  plant  must  not  escape  from  it 
too  freely,  and  hence  most  of  the  special  adaptations  are  to 
check  the  loss  of  water.  In  addition  to  this,  there  is  often 
developed  water-storage  tissue,  which  acts  as  a  reservoir, 
receiving  water  at  a  time  of  supply  and  doling  it  out  accord- 
ing to  the  needs  of  the  plant. 

Drought  conditions  vary  in  different  regions,  and  may 
be  grouped  under  three  heads:  (1)  possible  drought,  which 
occurs  at  irregular  intervals,  or  which  in  some  seasons  may 
not  occur  at  all;  (2)  periodic  drought,  which  occurs  at  regular 
intervals;  and  (3)  perennial  drought,  which  is  a  constant 
condition,  as  in  arid  or  desert  regions.  For  the  first  con- 
dition plants  are  poorly  prepared,  but  by  various  temporary 
expedients  may  resist  until  the  drought  ceases.  For  the 
second  condition  plants  are  well  prepared,  enduring  the 
regularly  recurring  drought  as  definitely  as  a  regularly  re- 
curring winter.  In  the  third  condition  plants  not  only  must 
endure  drought,  but  also  must  be  able  to  work  in  such  con- 
ditions. 

Some  of  the  conspicuous  methods  of  protection  against 
drought  have  been  described  (§  17).  These  should  be  kept 
in  mind  when  the  following  illustrations  of  xerophytic  asso- 
ciations are  considered. 

337 


338  A  TEXT-BOOK   OF  BOTANY 

202.  Rock  associations.— Certain  plants  are  able  to  live 
upon  rocks  and  boards  exposed  to  direct  sunlight.  The 
conspicuous  forms  are  lichens  and  mosses,  which  are 
found  very  commonly  splotching  rocks  (Fig.  308)  and  old 


FIG.  308. — Rocks  covered  with  lichens  and  mosses. 

fences.  Associated  with  them  are  often  crevice  plants, 
which  send  their  roots  into  crevices  and  so  gain  a  foot- 
hold. 

203.  Sand  associations. — The  plants  grouped  together 
on  dry,  sandy  ground  are  quite  different  in  appearance 
from  others,  and  such  areas  may  be  found  in  almost  every 
neighborhood,  at  least  along  streams.  On  certain  borders 
of  the  Great  Lakes  and  on  seacoasts  an  interesting  suc- 
cession of  sand  associations  occurs.  Nearest  the  water  is 
the  beach  with  such  a  poor  display  of  plants  that  it  looks 
bare. 

Beyond  the  beach  are  the  dunes,  which  are  billows  of 
sand  that  have  been  formed  by  the  prevailing  winds;  and  in 


XEROPIIYTES 


339 


many  cases  they  are  continually  changing  their  form  and 
are  frequently  movin«r  landward  (Fig.  309).  In  the  case  of 
these  moving  dunes  a  peculiar  type  of  vegetation  is  de- 
manded. Very  few  plants  are  able  to  live  in  such  severe 
conditions,  and  these  plants  have  developed  at  least  two  pe- 
culiar characteristics.  One  is  that  they  are  sand-binders; 
that  is,  the  underground  structures  are  extremely  far- 
reaching,  giving  the  plants  a  firm  anchorage  in  the  shifting 
sand.  As  soon  as  enough  of  the  sand-binders  have  es- 
tablished themselves,  a  shifting  dune  becomes  a  fixed  one. 
Another  characteristic  of  such  plants  is  that  they  are  able 


FIG.  309. — Dunes  of  Lake  Michigan  encroaching  landward,  in  this  case  diverting 
Calutaet  River. 


to  grow  up  through  the  sand  after  they  have  been  engulfed. 
Along  certain  coasts  where  moving  dunes  encroach  upon 
farms  and  villages  and  threaten  to  engulf  them,  great  at- 
tention has  been  given  to  checking  them  by  means  of  sand- 
binding  plants. 


340 


XEROPHYTES  341 

The  region  of  dunes  may  gradually  pass  landward  into 
sandy  stretches  or  fields,  covered  with  tufted  grasses, 
shrubs,  and  low  trees. 

204.  Plains. — Under  this  head  are  included  great  areas 
in  the  interior  of  continents,  where  dry  air  and  wind  prevail. 
The  plains  of  the  United  Stales  extend  from  about  the  one- 
hundredth  meridian  westward  to  the  foot-hills  of  the  Rocky 
Mountains.     Similar   great    areas   are    represented   by   the 
steppes  of  Siberia,  and   in   the  interior  of  all  continents. 
On  the  plains  of  the  United  States  the  characteristic  plant 
forms  are  bunch-grasses,  that  is,  grasses  which  grow  in  tufts 
and  do  not  form  turf;  and  the  low  grayish  shrubs  called 
sage-brush  (Fig.  310). 

205.  Cactus  deserts. — In  passing  southward  on  the  plains 
of  the  United  Slates,  the  conditions  are  observed  to  become 
drier,  until  the  cactus  deserts  are  reached  (Fig.  311).     This 
region  begins  in  western  Texas,  New  Mexico,  Arizona,  and 
Southern    California,    and    stretches    far    southward    into 
Mexico.     This  vast  arid  region  has  developed  a  peculiar 
flora,  which  contains  our  most  highly  specialized  drought 
plants.     The  numerous  forms  of  cactus  are  the  most  char- 
acteristic, and  associated  with  them  are  the  yuccas  and 
agaves.     Not  only  are  the  adaptations  for  checking  tran- 
spiration  and   for  retaining  water  of   the   most   extreme 
kind,  but  also  there  is  developed  a  remarkable  armature  of 
spines. 

206.  Subtropical  deserts. — In  these  areas  drought  con- 
ditions reach  the  greatest  extreme  in  the  combination  of 
great  heat  and  scanty  water-supply.     It  is  evident  that  such 
a  combination  is  almost  too  difficult  for  plants  to  endure. 
That  the  very  scanty  vegetation  is  due  to  lack  of  water, 
and  not  to  lack  of  proper  materials  in  the  soil,  is  shown  by 
the  fact  that  where  water  does  occur  oases  are  developed, 
in  which  luxuriant  vegetation  is  found.     The  desert  which 
stretches  from  Egypt  across  Arabia  may  be  regarded  as  a 


343 


23 


344  A  TEXT-BOOK  OF  BOTANY 

typical  one;  and  the  Desert  of  Sahara  is  another  well-known 
illustration. 

207.  Thickets. — Xerophytic     thickets     are     the     most 
strongly  developed  of  all  thicket  growths.     They  are  spe- 
cially characteristic  of  the  subtropics,  and  may  be  described 
as  scraggy,  thorny,  and  impenetrable.     Such  thickets  are 
well  displayed  in  Texas,  where  they  are  called  "chaparral "; 
and  similar  thickets  in  Africa  and  Australia  are  spoken  of 
as  "bush"  or  "scrub."     In  all  of  these  cases  the  thicket  is 
of  the  same  general  type,  and  is  one  of  the  most  forbidding 
areas  for  travel. 

208.  Forests. — The  most  common  xerophytic  forests  of 
the  United  States  consist  of  conifers,  especially  of  pines. 
They  occur  along  the  rocky  slopes  of  the  mountains,  and 
on  the  vast  sandy  areas  that  border  the  Great  Lakes  and 
cover  the  Gulf  States  (Fig.  312). 

209.  Salt  steppes. — In  these  areas,   not   only  are  the 
drought  conditions  continuous,  but  the  water  is  alkaline. 
The  salt  steppes  are  interior  dry  wastes  which  probably 
mark  the  site  of  old  sea  basins.     In  the  United  States  one 
of  the  most  extensive  of  the  salt  steppes  is  the  Great  Salt 
Lake  Basin.     Another  extensive  alkaline  waste  is  known  as 
the  Bad  Lands,  which  stretches  over  certain  portions  of 
Nebraska  and  South  Dakota. 

210.  Salt    and    alkaline    deserts. — In    these    areas    the 
water-supply  is  at  its  lowest  ebb,  and  therefore  is  saturated 
with  the  characteristic  salts  of  the  soil.     No  worse  com- 
bination for  plant  activity  can  be  imagined  than  the  com- 
bination of  scanty  water-supply  and  abundant  salts.     In 
consequence,  such  areas  are  almost,  if  not  absolutely,  devoid 
of  vegetation.     As  illustrations,  the  extensive  desert  of  the 
Dead  Sea  region  and  the  Death's  Valley  in  southern  Cali- 
fornia may  be  cited. 


CHAPTER  XXIV 

MESOPHYTES 

211.  General  characters. — Mcsophytes  include  the  com- 
mon vegetation  of  temperate  regions.     The  conditions  of 
moisture  are  medium,   precipitation  is  in  general  evenly 
distributed,  and  the  soil  is  rich  in  humus.       This  may  be 
regarded  as  the  normal  condition  for  plants.     It  is  certainly 
the  arable  condition,  and  best  adapted  to  the  plants  which 
men  cultivate.     When  for  the  purposes  of  cultivation  xero- 
phytic  areas  are  irrigated,  or  hydrophytic  areas  are  drained, 
it  is  simply  to  bring  them  into  mesophytic  conditions.     Con- 
spicuous among  mesophytir  associations  are  the  following: 

212.  Meadows. — This  term  must  be  restricted  to  natural 
meadow  areas,  and  should  not  be  confused  with  artificial 
areas  of  the  same  name  under  the  control  of  man.     The 
appearance  of  such  an  area  hardly  needs  description,  as  the 
vegetation  is  a  well-known  mixture  of  grasses  and  flowering 
herbs,  the  former  usually  predominating.     Such  meadows, 
of  large  or  small  extent,  are  very  common  in  connection 
with  forest  areas  and  on  the  flood-plains  of  streams  (Fig. 
313). 

The  greatest  meadows  of  the  United  States  are  the 
prairies,  which  extend  in  general  from  the  Missouri  east- 
ward to  the  forest  region  of  Illinois  and  Indiana.  The 
vegetation  of  the  prairies  is  usually  composed  of  tufted 
grasses  and  perennial  flowering  herbs  (Fig.  314).  Unfor- 
tunately most  of  the  natural  prairie  has  been  replaced  by 
farms,  and  the  characteristic  prairie  plants  are  not  easily 

345 


346 


347 


348  A  TEXT-BOOK  OF  BOTANY 

seen.  The  flowering  herbs  are  often  very  tall  and  coarse, 
but  have  brilliant  flowers,  as  asters,  golden  rods,  rosinweeds, 
lupines,  etc. 

The  origin  of  the  prairie  has  long  been  a  vexed  question, 
which  has  usually  taken  the  form  of  an  inquiry  into  the 
conditions  which  forbid  the  growth  of  a  natural  forest. 
Prairies  are  of  two  kinds  at  least :  those  due  to  soil  conditions 
and  those  due  to  climatic  conditions.  The  former  are  char- 
acteristic of  the  Eastern  prairie  region,  and  appear  in  scat- 
tered patches  through  the  forest  region  as  far  East  as  Ohio 
and  Kentucky.  They  are  probably  best  explained  as  re- 
presenting old  swamp  areas,  which  in  a  still  more  ancient 
time  were  ponds  or  lakes.  All  the  prairies  of  the  Chicago 
area  are  evidently  of  this  type,  being  associated  with  former 
extensions  of  Lake  Michigan. 

The  climatic  prairies  are  characteristic  of  the  West- 
ern prairie  region,  and  are  more  puzzling  than  the  others. 
Among  the  several  explanations  suggested,  perhaps  the 
most  prominent  is  that  which  regards  the  absence  of  a 
natural  forest  on  the  Western  prairies  as  due  to  the  prevail- 
ing dry  winds.  The  extensive  plains  farther  West  develop 
the  strong  and  dry  winds  that  sweep  over  the  prairies,  and 
this  brings  extremes  of  heat  and  drought,  in  spite  of  the 
character  of  the  soil.  In  such  conditions  a  seedling  tree 
could  not  establish  itself.  If  it  is  protected  through  this 
tender  period  it  can  maintain  itself  afterward.  These  prai- 
ries, therefore,  represent  a  sort  of  broad  beach  between  the 
Western  plains  and  the  Eastern  prairies  and  forests. 

213.  Thickets. — Mesophytic  thickets  are  not  so  im- 
penetrable as  xerophytic  thickets  (§  207),  an4  are  usually 
developed  as  forerunners  of  forests.  An  illustration  of  this 
may  be  obtained  by  noting  the  succession  of  plants  on  a 
cleared  area.  After  such  an  area  has  been  cleared  of  its 
trees,  it  is  overrun  by  herbs  that  develop  rapidly  from  the 
seed,  the  so-called  fireweed  usually  being  conspicuous. 


349 


350  A   TEXT-BOOK  OF  BOTANY 

Following  the  herb  associations,  there  is  a  gradual  invasion 
of  coarser  herbs  and  shrubby  plants,  forming  thickets; 
and  finally  a  forest  growth  may  appear  again. 

214.  Deciduous  forests. — Deciduous  forests  are  especially 
characteristic  of  temperate  regions,  the  deciduous  habit 
being  an  adaptation  to  the  regular  recurrence  of  winters. 
How  the  conifers  contrast  with  the  deciduous  trees  in  this 
regard  has  been  described  (§  19).  The  method  of  shedding 
leaves  (§  18),  the  characteristic  autumnal  coloration  (§  18), 
and  the  cultivation  of  the  vernal  habit  by  certain  asso- 
ciated herbs  (§  27)  have  all  been  considered.  The  decidu- 
ous forest  is  known  as  the  climax  vegetation  of  the  temper- 
ate regions,  replacing  all  other  associations  if  the  conditions 
become  favorable.  Even  a  forest  of  conifers  is  gradually 
replaced  by  a  deciduous  forest  when  the  conditions  become 
mesophytic. 

Deciduous  forests  may  be  pure  or  mixed.  A  common 
type  of  pure  forest  is  the  beech  forest,  which  is  a  dark  for- 
est, the  wide-spreading  branches  of  neighboring  trees  over- 
lapping so  as  to  form  a  dense  shade  (Fig.  315).  In  such 
a  forest,  therefore,  there  is  little  or  no  undergrowth.  An- 
other pure  forest,  which  belongs  to  drier  areas,  is  the  oak 
forest,  which  is  a  light  forest,  permitting  access  of  light  for 
lower  plants  (Fig.  316).  In  such  a  forest,  therefore,  there 
is  usually  more  or  less  undergrowth.  The  typical  American 
deciduous  forest,  however,  is  the  mixed  forest,  made  up  of 
many  varieties  of  trees,  such  as  beech,  oak,  elm,  walnut, 
hickory,  maple,  gum,  etc. 

Deciduous  forests  may  be  roughly  grouped  also  as  up- 
land and  flood-plain  (river  bottom)  forests, the  former  being 
less  luxuriant  and  containing  fewer  types,  the  latter  being 
the  highest  type  of  forest  growth  in  its  region  (Fig.  317). 
A  few  general  illustrations  may  be  given,  which  will  en- 
able the  student  to  characterize  the  forests  of  his  neighbor- 
hood. 


351 


FIG.  317. — A  mixed  river  bottom  forest  in  northern  Illinois. 

353 


MESOPHYTES 


353 


In  northern  Illinois  the  upland  forest  is  generally  made 
up  of  white  and  red  oaks  and  shellbark  hickory;  while  the 
flood-plain  forest  contains  twenty  to  twenty-five  tree  forms, 


•  is.  -Junction  between  an  upland  forest   (oaks  on  the  slope  to  the  right) 
and  a  flood-plain  forest  (on  the  level  ground  to  the  left). 

prominent  among  which  are  the  elms  (white  and  slippery), 
linden  (basswood),  cotton  wood,  ash,  silver  maple,  box-elder, 
walnut,  and  willows  (Fig.  318). 

Farther  south,  from  central  Illinois,  Indiana,  and  Ohio 
southward,  as  well  as  in  the  Alleghanies,  the  flood-plain 
forests  are  the  richest  known,  containing,  in  addition  to 
the  forms  enumerated  above,  such  prominent  trees  as  syca- 
more, beech,  sugar-maple,  tulip-tree  (white  poplar),  buck- 
eye, hackberry,  honey-locust,  coffee-tree,  etc. 

In  Michigan  and  Wisconsin  the  upland  forests  consist 
prominently  of  beech,  sugar-maple,  and  hemlock,  a  char- 
acteristic mixture  of  deciduous  and  evergreen  trees;  while 
the  flood-plain  forests  are  scarcely  at  all  developed. 


354 


.M  KSOPEYTES 


355 


In  the  Alleghany  region  and  New  England  the  upland 
forests  arc  very  extensive  and  complicated,  grading  from 
the  rich  flood-plain  forests  of  the  lower  levels  to  the  strict  ly 
xerophytic  forests  (pines  and  black  oaks)  of  the  higher  lev- 
els, and  dominated  l>y  various  oaks,  chestnuts,  and  hick- 
ories. 

The  flood-plain  forests  of  New  Kngland  are  not  so  rich 
as  those  of  the  Alleghany  region  and  the  central  West,  the 
dominant  forms  being  elm. 
linden,  ash,  maple,  syca- 
more, tulip-tree,  etc. 

iM.").  Tropical  forests. - 
The  forests  of  the  rainy 
tropics  may  be  regarded  as 
the  climax  of  the  world's 
vegetation  (Fig.  319),  for 
the  conditions  favor  con- 
stant plant  activity  at  the 
highest  possible  pressure. 
Such  great  forest  growths 
are  found  within  the  region 
of  the  trade-winds,  where 
there  is  heavy  rainfall,  great 
heat,  and  very  rich  soil,  as 
in  the  East  Indies,  and 
along  the  Amazon  and  its 
tributaries.  So  abundant 
is  the  precipitation  that  the 
air  is  often  saturated  and 
the  plants  drip  with  the 
moisture. 

The  striking  characteris- 
tics of  the  great  mixed  trop- 
ical forest  are  as  follows:  (1)  There  is  no  regular  period  for 
the  development  or  fall  of  leaves,  and  hence  there  is  no  time 


FIG.  320.— A  gutter-pointed  leaf  of  a  rainy 
foi-f.-t.      After  SCHIMPER. 


356  A  TEXT-BOOK  OF  BOTANY 

of  bare  forest  or  of  forests  just  putting  out  leaves.  Leaves 
are  continually  being  shed  and  formed,  but  the  trees  always 
appear  in  full  foliage.  (2)  The  density  of  growth  is  remark- 
able, resulting  in  a  gigantic  jungle,  with  plants  at  every 
level,  interlaced  by  great  vines  and  covered  by  perching 
plants.  (3)  Such  forests  display  not  only  an  immense  num- 
ber of  individual  plants,  but  also  an  extraordinary  num- 
ber of  species.  (4)  The  various  devices  for  shedding  the 
abundant  rain  from  the  leaves  give  to  them  a  very  charac- 
teristic appearance.  Prominent  among  them  are  the  gut- 
ter-pointed leaves,  the  tip  being  prolonged  as  a  sort  of 
spout  and  the  veins  depressed,  the  whole  surface  of  the  leaf 
resembling  a  drainage  system  (Fig.  320). 


INDEX 


Absorption,  78,  86. 

Adaptation,  328,  337. 

Air  pores,  168. 

Air  roots,  82. 

Air  spaces,  18. 

Akene,  239. 

Aleurone  grains,  89. 

Alfalfa,  293. 

Algae,    98,    165;    blue-green,    98; 

brown,  116;  green,  102;  red,  124. 
Alga-like  Fungi,  144. 
Alternation   of  generations,    is:?; 

fern,  196;  liverwort,  171;  moss, 

180. 

Amaryllidaceae,  278. 
Ament,  283. 
Angiosperms,  220. 
Annual  rings,  54. 
Anther,  224. 
Antheridium,     Bryophyte,     184; 

fern,  193;  Fucus,  124;  liverwort, 

169;   mildew,    145;    moss,    177; 

(Edogonium,  110;  Peronospora, 

143;  red  Algae,  127;  Selaginella, 

204;  Vaucheria,  112. 
Anthoceros,  173,  183. 
Antitoxin,  135. 
Apples,  289. 
Apricots,  288. 
Arbor  Day,  323. 
Archegonium,     Bryophyte,     184; 

conifer,  216;  fern,  193;  livenvort, 

169;  moss,  177;  Selaginella,  205. 


Archichlamydeae,  282. 
Ascomycetes,  146. 
Ascus,  146. 
Assimilation,  88. 

Associations,  324;  see  Plant  asso- 
ciations. 
Axil,  42. 

Bacteria,  130;  disease,  134,  135; 
fermentation,  134;  nitrogen  fix- 
ation, 134,  135;  reproduction, 
132;  resistance,  133;  root-tuber- 
cles, 136;  spores,  133;  structure, 
131. 

Bamboo,  271. 

Banana,  280. 

Bark,  55. 

Barley,  267. 

Basidia,  155. 

Basidiomycetes,  158. 

Bast,  51;  root,  74. 

Bean,  294. 

Berry,  239,  286,  298. 

Big  tree,  219. 

Blackberry,  287. 

Black  knot,  147. 

Blade,  6. 

Blueberry,  303. 

Blue-green  Algae,  98. 

Bog  moss,  181. 

Bracket  Fungi,  156. 

Branches,  root,  76. 

Brown  Algae,  116. 
357 


358 


INDEX 


Bryophytes,  183,  208. 

Bud,  67;  accessory,  69;  adventi- 
tious, 70;  axillary,  68;  flower, 
68;  leaf,  68;  naked,  69;  scaly, 
35,  69;  terminal,  68. 

Budding,  317;  of  cells,  138. 

Bulb,  66;  self-burial,  67. 

Bulblet,  66. 

Buttercup,  284. 

Cactus  desert,  341. 

Calyx,  221. 

Cambium,  53;  cork,  54;  roots,  75. 

Cantaloupe,  314. 

Caprification,  252. 

Caprifig,  252. 

Capsule,  239. 

Carbohydrate,  18. 

Carpel,    226;    Angiosperms,    221; 

Conifers,  214. 
Catkin,  283. 
Cedar-apple,  152. 
Cell,  15,  103. 
Cellulose,  103. 
Cell-wall,  103. 
Cereal,  264. 
Chaparral,  344. 
Cherry,  289. 
Chlorophycese,  102. 
Chlorophyll,  22. 
Chloroplast,    17,    104;    Spirogyra, 

113. 

Chocolate,  301. 
Cinchona,  309. 
Citron,  300. 
Citrous  fruits,  299. 
Cladophora,  108. 
Clay,  77. 

Clinging  roots,  81. 
Cloves,  292. 
Club-moss,  200. 
Cluster-cup,  151. 


Coal,  205. 

Coconut-palm,  274. 

Coenocyte,  111. 

Coffee,  308. 

Compass  plant,  29. 

Composite,  310. 

Composites,  310. 

Cone,  carpellate,  214;  staminate, 

213. 

Conferva  forms,  116. 
Conifers,  211. 
Conjugate  forms,  116. 
Conjugation,  107. 
Coral  Fungi,  157. 
Cork  cambium,  54. 
Corn,  268. 
Corolla,  221. 
Cortex,  50. 
Cotton,  295. 

Cotyledon,  85;  escape  of,  91. 
Cranberry,  302. 
Crossing,  254,  317. 
Cross-pollination,  245. 
Crucifera,  286. 
Cucumber,  314. 
Cucurbitacese,  314. 
Currant,  298. 
Cuticle,  26. 
Cutting,  317. 
Cyanophyceae,  98. 
Cycads,  216. 
Cytoplasm,  104. 

Darlingtonia,  37. 

Date-palm,  275. 

Deciduous  forest,  350. 

Deciduous  habit,  32. 

Desert,  Cactus,  341;  salt  and  al- 
kaline, 344;  subtropical,  341. 

Diastase,  88. 

Dicotyledons,  50,  230,  282;  em- 
bryo, 237;  Sympetalae,  302. 


INDEX 


359 


Differentiation,  102. 
Digestion,  87. 
Dion;iia,  40. 

B,  bacteria,  134,  135. 
Disk,  310. 
Dotted  duct,  53. 
Downy  mildew,  142. 
Drosera,  38. 
Drought,  337. 
Drought  plants.  32U. 
Drupe,  239,  288. 
Dune,  338. 

Krt  ocarpus,  120. 

Egg,  Angiosperms,  235;  CEdogo- 

nium,  110. 
Embryo,   85;    Angiosperms,   230; 

Conifers,  217. 

Kndosperm,  SO;  Conifers,  218. 
Enzyme,  88. 
Epidermis,  leaf,  15,  24;  Marehan- 

tia,  167;  stem,  50. 
Epiphyte,  82. 
Equisetum,  197. 
EriracesR,  302. 
Evergreens,  33. 

Family,  262. 

Fat,  89. 

Fermentation,  bacteria,  134; 
yeasts,  138. 

Ferns,  183;  antheridia,  193;  ar- 
chegonia,  193;  fertilization,  195; 
gametophyte,  193;  general  char- 
acters, 184;  leaves,  187;  life- 
history,  187,  196;  sperms,  194; 
sporangia,  191;  sporophyte,  187, 
195;  vascular  system,  188. 

Fertilization,     107;     Angiosperm, 

236;    conifer,    216;    fern,    195; 

Fucus,     124;     liverwort,      169; 

Mucor,  142;  CEdogonium,   110; 

24 


Peronospora,  143;  red  Algae, 
126;  rusts,  152;  Spirogyra,  114; 
Ulothrix,  107. 

Fiber,  295. 

Fig,  pollination,  252. 

Figwort,  pollination,  249. 

Filament,  22  J. 

Fl:i\,  296. 

Flower,  220;  apocarpous,  284; 
bilabiate,  223;  cleistogamous, 
243;  clusters,  232;  dioacious, 
230;  Epigynous,  231;  hypogy- 
nous,  231;  insects,  242;  monoe- 
cious, 230;  n:ik<>d,222;  numbers, 
229;  papilionaceous,  291 ;  pistil- 
late, 230;  protandrous,  250;  pro- 
togynous,  250;  staminate,  230; 
sympetalous,  223. 

Foliage  leaves,  34. 

Forest,  deciduous,  350;  protective, 
322 ;v  rescrv:it  ions.  322;  supply. 
321;  tropical,  355;  xerophytic, 
344. 

Forestry,  320. 

Frond,  64,  187. 

Fruit,  238. 

Fucus,  118,  122. 

Fungi,  129,  165. 

Gametangium,  122. 

(Jamete,  107. 

Gametophyte,    171;    Angiosperm, 

235;  Conifer,  215;   Equisetum, 

200;    fern,    193;    Lycopodium, 

202;  Selaginella,  204. 
Genus,  262. 
Geotropism,  90. 
Germination,  conditions,  86;  seed, 

84,  218. 
Gills,  155. 
Girdling,  55. 
Glosocapsa,  98. 


360 


INDEX 


Gooseberry,  298. 

Gourd  fruit,  314. 

Grafting,  56,  317. 

Grafts,  317. 

Grain,  239. 

Gramineae,  263. 

Grape,  298. 

Grape-fruit,  299. 

Grasses,  263. 

Green  Algae,  102. 

Green  felt,  111. 

Green  slime,  101. 

Growth,  leaf,  23;  root,  76;  stem, 

59. 

Guard-cells,  16. 
Gulf  weed,  118. 
Gymnosperms,  50,  207;  general 

character,  210. 

Hair,  26. 

Hay  grass,  271. 

Head,  234. 

Heaths,  302. 

Heliotropism,  93. 

Hemp,  297. 

Heredity,  316. 

Heterocyst,  100. 

Heterospory,  207;  Selaginella,  204. 

Horsetails,  197. 

Host,  129. 

Houstonia,  pollination,  250. 

Huckleberry,  303. 

Humus,  77. 

Hybrid,  253,  317. 

Hydrophytes,  326,  328. 

Hydrotropism,  90. 

Hypocotyl,  85;  escape  of,  89. 

Indusium,  191. 
Insects  and  flowers,  242. 
Integument,  229. 
Internode,  41. 


Involucre,  310. 
Iodine,  source,  120. 
Iridaceae,  278. 
Irish  moss,  source,  126. 
Iris,  pollination,  247. 
Irritability,  90. 

Jungermannia,  172. 

Keel,  247,  291. 
Kelp,  117. 

Labiatae,  223,  307. 

Labiates,  307. 

Laminaria,  117. 

Lawn  grass,  271. 

Layering,  47,  317. 

Leaf,  arrangement,  5;  autumnal 
colors,  33;  Bryophyte,  184;  de- 
ciduous, 32;  evergreen,  33;  fall, 
32;  fern,  187;  foliage,  34;  form,  7; 
growth,  23;  gutter-pointed,  356; 
horizontal,  9;  mosaic,  13;  motile, 
30;  night  position,  32;  parts,  6; 
profile,  29;  protection,  24;  rain, 
32;  relation  to  light,  8;  rosette 
habit,  11;  shading,  10;  special 
forms,  34;  structure,  15;  vena- 
tion, 6;  water  reservoir,  29. 

Leafy  axis,  erect,  181. 

Leafy  liverworts,  172. 

Legume,  239. 

Legumes,  291. 

Leguminosae,  239,  291;  pollination, 
246. 

Lemon,  300. 

Liana,  48. 

Lichen,  160. 

Life-history,  moss,  176;  mushroom. 
153;  red  Algae,  127;  rusts,  149; 
Selaginella,  205;  Ulothrix,  107. 

Life-relations,  3. 


INDEX 


361 


Light,  plant  associations,  326. 
Liliaceic,  277. 
Lilies,  277. 
Lime,  300. 
Liverworts,  165. 
Lucerne,  293. 
Lycopodium,  202. 
Lycopods,  201. 

Madders,  307. 

Maize,  268. 

Male  cell,  235. 

Mandarin,  '_)(.M>. 

Mangrove  swamp,  336. 

Maple  sap,  58. 

Man-bant  ia,  167. 

Meadows,  345. 

Megaspore,  Angiosperm,  235;  coni- 
fer, 214;  Selaginella,  205. 

Mesophyll,  17. 

Mesophytes,  327,  345. 

Microbe,  130. 

Micropyle,  229. 

Microspore,  conifers,  212;  Sela- 
ginella, 205. 

Mildew,  144;  downy,  142. 

Midrib,  7. 

Mold,  black,  139. 

Monocotyledons,  50,  56,  230; 
classification,  262 ;  embryo, 
237. 

Morel,  148. 

Mosaic,  13. 

Moss,  175 ;  flower,  177 ;  groups, 
181. 

Motile  leaves,  30. 

Mucor,  139. 

Mushroom,  153. 

Muskmelon,  314. 

Mustard  Family,  286. 

Mycelium,  140. 

Mycorhiza,  159. 


Nectar,  36,  242. 
Needle-leaves,  211. 
Nepenthes,  38. 
Nightshades,  304. 
Nitrogen  fixation,  134,  135. 
Node,  5,  41. 
Nostoc,  99. 
Nucellus,  229. 
Nucleus,  103. 
Nutmeg  melon,  314. 
Nutrition,  3. 

Oats,  266. 

(Edogonium,  108. 

Olive,  313. 

Oogonium,    Fucus,    124;    mildew, 

145;  (Edogonium,  110;  Perono- 

spora,     143;    red    Algae,     126; 

Vaucheria,  112. 
Oospore,  107. 
Orange,  299. 
Orchidaceae,  278. 
Orchids,  278;  pollination,  248. 
Organ,  3. 
Oscillatoria,  100. 
Osmosis,  79. 
Ovary,  227. 
Ovule,  Angiosperm,  228;  conifer 

214. 

Palisade  layer,  25. 
Palisade  tissue,  17. 
Palms,  271. 
Pappus,  310. 
Parasite,  129. 
Pasture  grass,  271. 
Pea,  293. 
Peach,  288. 
Peanut,  294. 
Pear,  291. 

Peat,  175;  bogs,  336. 
Perianth,  222. 


362 


INDEX 


Peronospora,  142. 

Petal,  221,  222. 

Petiole,  6. 

Phseophyceae,  116. 

Phloem,  52;  root,  74. 

Photosynthesis,  18,  87. 

Phototropism,  92. 

Phycomycetes,  144. 

Pileus,  155. 

Pine,  timber,  218. 

Pineapple,  281. 

Pirus,  289. 

Pistil,  228. 

Pitcher-plant,  35. 

Pith,  50;  ray,  51. 

Plains,  341. 

Plant  associations,  324;  cactus 
desert,  341;  deciduous  forest, 
350;  mangrove  swamp,  336; 
meadow,  345;  mesophytic  thick- 
et, 348;  peat-bog,  336;  plain, 
341;  pond  weed,  328;  reed- 
swamp,  331;  rock,  338;  salt  and 
alkaline  desert,  344;  salt  marsh 
and  meadow,  336;  salt  steppe, 
344;  sand,  338;  subtropical 
desert,  341;  swamp,  331;  swamp 
forest,  336;  swamp  thicket,  332; 
tropical  forest,  355;  xerophytic 
forest,  344;  xerophytic  thicket, 
344. 

Plant-breeding,  316. 

Plasmolysis,  115. 

Plastid,  104. 

Pleurococcus,  102. 

Plum,  289. 

Plumule,  86;  escape  of,  91. 

Pod,  238. 

Pollarding,  70. 

Pollen,  242;  Angiosperm,  224; 
conifer,  212. 

Pollen-sac,  226;  conifer,  212. 


Pollen-tube,     Angiosperm,     236; 

conifer,  217. 
Pollination,      Angiosperm,      242; 

conifer,  217. 
Pollinium,  248. 
Pome,  289. 
Pomelo,  299. 
Pomology,  289. 
Pond-scum,  113. 
Pondweed  association,  328. 
Pore  Fungi,  156. 
Potato,  305. 
Prairie,  345. 
Profile  leaves,  29. 
Pronuba  and  Yucca,  244. 
Prop-root,  80. 
Protection,  leaves,  24. 
Proteid,  88. 
Prothallium,  193. 
Prothallus,  193. 
Protoplasm,  87,  103. 
Prune,  289. 
Prunus,  288. 

Pteridophytes,  183,  207,  208 
PurTball,  158. 
Pumpkin,  315. 
Pyrenoid,  114. 

Quince,  291. 
Quinine,  309. 

Raceme,  232. 
Rain,  leaves,  32. 
Ranunculacese,  284. 
Raspberry,  287 . 
Ray,  310. 
Reaction,  93. 
Receptacle,  240. 
Red  Alga3,  124. 
Redwood,  219. 
Reed  swamp,  331. 
Reforestation,  323. 


INDEX 


363 


Reproduction,  3;  asexual,  107; 
blue-green  Algae,  101;  red  Algae, 
126;  sexual,  107;  vegetative 
multiplication,  101. 

Reservations,  forest,  322. 

Resin,  219. 

Kopiration.  s7. 

Rhi/oid,  HIT. 

Rhi/ome,  03;  self-burial,  G7. 

Rhodophyceae,  1'Jl. 

Hil»,  7. 

Riccia,  172. 

Ricciocarpus,  172. 

Rice,  269. 

Rockweed,  118. 

Root,  71;  absorption,  78;  air,  82; 
bast,  74;  branch,  7<>;  cambium, 
75;  cliniring.  M;  cuttings.  70; 
growth,  7<>;  diameter  increase, 
75;  hair,  71;  internal  structure. 
74;  phloem,  74;  primary,  72; 
prop,  80;  secondary,  72;  special 
forms,  80;  tap,  7~;  vascular 
cylinder,  74;  water,  80;  wood, 
71;  xylem,  74. 

Root-cap,  73. 

Root-cuttings,  70. 

Root-fungus,  159. 

Root-hair,  74,  7v 

Root-pressure,  ~»v 

Rootstock,  63;   self-burial,  67. 

Root-tubercles,  13<i. 

Rosaceae,  286. 

Roses,  286. 

Rosette-habit,  11,  28. 

Rubiaceae,  307. 

Runner,  47. 

Rust,  149. 

Rye,  266. 

Sac  Fungi,  146. 
Sago-palm,  276. 


Salt  marsh,  336. 
Salt  meadow,  336. 
Salt  steppe,  344. 

Sand,  77. 

Sand-binder,  339. 

Sap,  Meent,  -"'7;  maple,  58. 

Saprophyte,  !_".>. 

Sargassum,  119. 

Sarracenia,  35. 

Scale.  I'li.  31. 

Srinn.  60. 

Scouring  rush,  198. 

Sea  lettuce,  110. 

Seed,    absorption    of   water,    80; 

Aniriosperiu,  '-37;  conifer,  217; 

disper.-al.  -J.Vi;  germination,  84, 

218;  structure.  B4. 
Seed-dispersal,      L'55;      air.      -J.r.7: 

animals.    L'C.O;    discharge,    255; 

\\  ater,  259. 
Selaginella,  203. 

Select!..!..  818. 

Self-burial,  07. 

Self-pollination,  243. 

Sensitive  plant,  30. 

Sepal,  221. 

Sequoia.  211,  219. 

Shaddock,  299. 

Shade-plant.  320. 

Shoot,  41. 

Sieve  plate,  53. 

Sieve  vessel,  53. 

Siphon  forms,  110. 

Societies,  324. 

Soil,  77. 

Solanaoesp,  304. 

Sorus,  191. 

Species,  203. 

Sperm,  Angiosperm,  235;  conifer, 
•Jill;  cycad,  211;  fern,  194; 
liverwort,  109;  moss,  177;  CEdo- 
gonium,  110;  red  Algae,  120. 


364 


INDEX 


Spermatophytes,  208. 

Spike,  232. 

Spirogyra,  113. 

Spongy  tissue,  18. 

Sporangium,  Angiosperm,  224; 
brown  Algse,  121;  conifer,  212; 
Equisetum,  199;  fern,  191; 
Mucor,  141;  red  Algse,  126; 
Selaginella,  203. 

Spore,  106;  Angiosperm,  224,  235; 
brown  Algae,  121;  Equisetum, 
199;  green  Algae,  106;  mildew, 
145;  (Edogonium,  108;  red  Algae, 
126;  rusts,  149,  151;  swimming, 
106;  Vaucheria,  112. 

Spore-case,  moss,  180. 

Spore-fruit,  mildew,  146;  red 
Algee,  126. 

Sporophyll,  207;  Equisetum,  199. 

Sporophyte,  171;  Anthoceros,  173; 
conifer,  215;  club-moss,  202; 
fern,  187,  195;  Jungermannia, 
173;  leafy,  207;  Lycopodium, 
202;  Marchantia,  170;  moss, 
179. 

Spring  flowers,  67. 

Spur,  223. 

Squash,  315, 

Stamen,  224;  Angiosperm,  221; 
conifer,  212. 

Standard,  291. 

Starch,  21. 

Stem,  41;  annual,  53;  climbing, 
47;  direction,  42;  erect,  42;  ex- 
ternal structure,  41;  growth,  59; 
internal  structure,  50;  perennial, 
53;  prostrate,  45;  special  forms, 
59. 

Steppes,  344. 

Stigma,  227. 

Stimulus,  90. 

Stipe,  155. 


Stipule,  6. 

Stock,  56,  317. 

Stoma,  16. 

Stone-fruit,  239,  288. 

Strawberry,  286. 

Strobilus,  club-moss,  202;  conifer, 
212;  Equisetum,  198;  Lycopo- 
dium, 202;  Selaginella,  203. 

Style,  227. 

Subsoil,  78. 

Subtropical  desert,  341. 

Sucker,  70. 

Sugar-cane,  270. 

Summer  spore,  149. 

Sundew,  38. 

Swamp,  331;  forest,  336;  thicket, 
332. 

Sweet  potato,  313. 

Swimming  spore,  106. 

Sympetalae,  223,  282,  302. 

Tangerine,  299. 

Tap-root,  72. 

Tea,  300. 

Temperature,   plant   associations, 

325. 

Tendril,  35,  48,  60. 
Testa,  85,  218,  237. 
Tetraspore,  126. 
Thallophytes,  165,  183,  208. 
Thicket,    mesophytic,   348;   xero- 

phytic,  344. 
Thorn,  35,  62. 
Timber,  conifer,  218;  hardwood, 

284. 

Toadstool,  153. 
Tobacco,  306. 
Tomato,  306. 
Tracheary  vessels,  52;  annular,  52; 

dotted,  53;  pitted,  53;  spiral, 

52. 
Transpiration,  22. 


INDEX 


365 


Tree  group,  282. 
Tropical  forest,  355. 
Truffle,  147. 

Tuber,  65;  self-burial,  67. 
Tumbleweed,  257. 
Turgor,  104. 
Turpentine,  219. 
Twiner,  47. 

Ulothrix,  105. 
Umbel,  233. 
UmbellifenB,  294. 

Vacuole,  115. 

Variation,  316. 

Vascular  bundle,  51. 

Va-ruUir  cylinder,  50,  74. 

Vascular  system,  76;  fern,  188. 

Vaurheria,  111. 

Vegetative  multiplication,  101. 

Vegetative  propagation,  316. 

Vein,  IS,  53. 

Venation,  6. 

Venus  fly-trap,  40. 

Vernal  habit,  67. 

Viticulture,  298. 


Water,   absorption   by   root,   78; 

absorption  by  seed,  86;   plant 

associations,  324. 
Watermelon,  314. 
Water  plants,  326. 
Water  reservoirs,   in  plants,   29; 

pollution  of,  102. 
Water-root,  80. 
Water-sprout,  70. 
Wheat,  264. 
Wheat  rust,  149. 
White  pine,  timber,  218. 
Wind,  plant  associations,  326. 
Wings,  291. 
Winter  spore,  150. 
Wood,  51;  root,  74. 
Wounds,  healing,  55. 
Wrack,  118. 

Xerophytes,  326,  337. 
Xylem,  51;  root,  74. 

Yeast,  138. 

Yellow  pine,  timber,  218. 

Yucca,  pollination,  244. 

Zygospore,  107. 


(9, 


NATURE  STUDY  AND  AGRICULTURE 

Practical  Nature  Study  and  Elementary 
Agriculture 

A  Manual  for  the  Use  of  Teachers  and  Normal  Students. 

By  JOHN  M.   COULTER,  Director  of  the  Department  of 

Botany,    University   of   Chicago :     TQHN    G.    COULTER, 

Professor  of  Biology, 

ALICE    JEAN    PATTERs^w^iftepartment    ofjo,    in 

charge  of  Nature  Studp,  Illinois  State  Normal  Univemity. 

1 2 mo,  cloth,  $1.35  ne\^  / 

This  hook  is  an  attempt,  oft^ry4&fJ£^  (QeXj^^lp  the 

teacher  of  nature  study  to  1 in  IMT)MT  inih  |l(  lllliinT^Triii  work, 

and  to  make  his  work  more  definite.  The  volume  has  grown  out 
of  the  experience  of  the  authors.  The  material  has  largely  been 
used  in  regular  class  work,  and  found  efficient  under  conditions 
similar  to  those  of  the  average  school. 

Part  I  is  devoted  to  presenting  the  principles  of  nature  study, 
its  mission  and  spirit,  as  well  as  the  dangers  which  the  study  entails 
and  how  to  avoid  them.  It  is  practically  a  guide  to  the  teaching  of 
nature  study.  Part  II  contains  a  detailed  topical  outline  by  grades 
and  seasons  of  the  materials  used  in  nature  study  in  the  training 
school  at  the  Illinois  State  Normal  University.  Its  definite  outlines 
of  work  will  be  of  important  service  to  teachers  who  are  called  upon 
to  handle  the  subject  with  slight  previous  training.  Part  III  is 
principally  devoted  to  an  outline  course  for  elementary  agriculture 
in  the  seventh  and  eighth  grades,  with  most  of  the  lessons  worked 
out  in  detail.  These  lessons  have  all  satisfactorily  met  the  test 
of  class-room  use.  Part  IV  comprises  certain  chapters  on  more 
general  topics — material  which  will  prove  serviceable  for  teachers 
whose  general  science  training  has  been  slight  or  is  lacking  entirely. 
The  aim  is  to  provide  a  scientific  point  of  view  of  the  materials  and 
principles  which  are  to  be  used  in  the  work. 

The  study  of  this  exceedingly  practical  book,  the  aim  of  which 
is  to  aid  in  making  nature  study  practical  under  present  teaching 
conditions,  should  produce  better  teachers  and  more  enlightened 
students. 

D .     APPLETON     AND     COMPANY 

NEW  YORK  CHICAGO 


TWENTIETH  CENTURY  TEXT-BOOKS. 


TEXT-BOOKS  OF  ZOOLOGY. 

By  DAVID  STARR  JORDAN,  President  of  Leland  Stan- 
ford Jr.  University;  VERNON  LYMAN  KELLOGG,  Professor 
of  Entomology;  HAROLD  HEATH,  Assistant  Professor  of 
Invertebrate  Zoology. 

Evolution  and  Animal  Life. 

This  is  a  popular  discussion  of  the  facts,  processes,  laws,  and  theories 
relating  to  the  life  and  evolution  of  animals.  The  reader  of  it  will  have 
a  very  clear  idea  of  the  all-important  theory  of  evolution  as  it  has  been 
developed  and  as  it  is  held  to-day  by  scientists.  8vo.  Cloth,  with  about 
300  illustrations,  $2.50  net ;  postage  20  cents  additional. 

Animal  Studies. 

A  compact  but  complete  treatment  of  elementary  zoology,  especially 
prepared  for  institutions  of  learning  that  prefer  to  find  in  a  single  book 
an  ecological  as  well  as  morphological  survey  of  the  animal  worlH.  i2mo. 
Cloth,  $1.25  net. 

Animal  Life. 

An  elementary  account  of  animal  ecology — that  is,  of  the  relations 
of  animals  to  their  surroundings.  It  treats  of  animals  from  the  stand- 
point of  the  observer,  and  shows  why  the  present  conditions  and  habits 
of  animal  life  are  as  we  find  them.  I2mo.  Cloth,  f  1.20  net. 

Animal  Forms. 

This  book  deals  in  an  elementary  way  with  animal  morphology.  It 
describes  the  structure  and  life  processes  of  animals,  from  the  lowest 
creations  to  the  highest  and  most  complex.  I2mo.  Cloth,  $1.10  net. 

Animals. 

This  consists  of  "Animal  Life"  and  "Animal  Forms"  bound  in  one 
volume.  I2mo.  Cloth,  $1.80. 

Animal  Structures. 

A  laboratory  guide  in  the  teaching  of  elementary  zoology.  I2mo. 
Cloth,  50  cents  net. 

D.     APPLETON     AND     COMPANY, 

NEW  YORK.       BOSTON.       CHICAGO.       LONDON. 


TWENTIETH  CENTURY  TEXT-BOOKS. 


An  Introduction  to  Physical  Geography. 

By  GROVE  KARL  GILBERT,  LL.  D.,  United  States  Geological  Sur- 
vey ;  Author  of  "The  Geology  of  the  Henry  Mountains,"  "Lake 
Bonneville,"  Numerous  Reports,  etc.,  in  publications  of  United 
States  Geological  Survey;  and  ALBERT  PERRY  BRIGHAM,  A.M.. 
Professor  of  Geology,  Colgate  University,  Hamilton,  N.  Y.,  Fellow 
of  the  Geological  Society  of  America,  etc.,  Associate  Editor  Bulletin 
American  Geographical  Society,  Author  of  "A  Text-Book  of 
Geology "  (Twentieth  Century  Text- Books).  Illustrated.  I2mo. 
Cloth,  $1.25. 

SIX    SALIENT    POINTS. 

The  new  pedagogy  of  Physical  Geography  receives  in  this  book  its  first 
adequate  presentation. 

Hence,  this  text  meets  the  present  requirements  of  high  school  and 
college-entrance  work  perfectly  and  in  full  detail. 

Treatment  adapted  to  the  early  years  of  the  course— the  book  will  interest 
pupils  aged  fourteen. 

Statements  throughout  are  not  merely  theoretical,  but  definitely  concrete, 
appropriately  illustrated,  and  logically  summarized. 

Topics  cover  "The  Physical  Environment  of  Man:"  The  Earth  as  a 
Globe,  the  Ocean,  the  Air,  and  the  Land — in  increasing  proportion. 

The  exquisite  half-tone  illustrations  far  surpass  in  beauty,  helpfulness, 
and  number  anything  before  attempted.  A  most  important  and  significant 
feature. 

THE   IDEAL   COURSE   AND   GILBERT  AND 

BRIGHAM'S   BOOK. 

This  book  meets  fully,  in  minute  detail,  and  for  the  first  time,  all 
the  specifications  set  forth  in  the  Report  of  the  Committee  on  College 
Entrance  Requirements  to  the  National  Educational  Association  in 
1899.  It  keeps  accurately  to  the  definition  laid  down  ;  it  furnishes  the 
requisite  kind  and  amount  of  instruction  to  train  the  observation  and 
to  prepare  for  later  special  courses  in  science ;  and  it  elevates  physical 
geography  beyond  cavil  to  the  proper  plane  for  a  college-entrance 
requirement,  by  organizing  its  content  to  its  highest  capacity  as  a 
pedagogic  discipline. 

D.    APPLETON     AND    COMPANY,     NEW    YORK. 


TWENTIETH    CENTURY    TEXT-BOOKS. 
A  Text-Book  of  Geology. 

By  Professor  ALBERT  PERRY  BRIGHAM,  of  Colgate  Uni 
versity.  477  Pages.  295  Illustrations.  12010.  Cloth,  $1.40. 

This  superb  text-book  is  the  best  account  for  secondary 
schools  of  the  earth's  marvelous  origin,  of  the  processes  that 
brought  the  ordered  world  out  of  chaos,  and  of  the  phenomena 
of  geologic  evolution — considered  dynamically,  structurally,  and 
historically.  The  planet's  life  history  is  told  with  directness, 
brevity,  and  pedagogic  fitness.  The  text  is  supplemented  with 
295  exquisite  photographic  illustrations,  many  taken  by  Professor 
Brigham  for  this  work.  An  exceptional  success  in  text-book 
writing  and  text-book  making. 

"  Brigham's  Geology  is  the  cleanest  eut  and  best  pedagogical  text- 
book for  the  high  school  that  I  have  seen." — C.  H»  Richardson, 
Hanover ',  N.  H. 

14  Most  interesting.  Decidedly  the  most  practical  book  that  I 
have  seen  for  use  in  high  schools." — Miss  S.  A.  Edwards,  Philadelphia 
High  School  for  Girls. 

I  consider  it  the  best  written  and  best  illustrated  book  I  hav*  ever 
seen  for  secondary  schools." — C.  F.  Warner,  Mechanics  Arts  High 
School^  Springfield,  Mass 

"  The  most  attractive  text-book  of  Geology  for  secondary  sphools 
that  I  have  seen.  The  illustrations  are  a  delight." — Belle  Sherman, 
Ithaca  High  School,  Ithaca,  N.  Y. 

"  It  is  magnificent.  I  consider  it  superior  to  any  other  book  of  the 
kind  in  illustrations,  text,  and  adaptation  to  field  work." — Mrs.  L.  L. 
W.  Wilson,  Philadelphia  Normal  School. 

"  In  every  way  fully  equal  to  any  of  the  splendid  series  of  Twen- 
tieth Century  Text-Books.  Many  of  the  illustrations  are  new  and 
their  execution  is  perfect." — R.  I.  Schiedt,  Professor  of  Geology 
Franklin  and  Marshall  College,  Lancaster,  Pa. 


D.     APPLETON    AND     COMPANY,     NEW     YORK. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


RENEWED  BOOKS  ARE  SUBJECT  TO  IMMEDIATE 
RECALL 


JUN2    1968 

Y25RECD 


LIBRARY,  UNIVERSITY  OF  CALIFORNIA,  DAVIS 

Book  Slip-14,800-8,'66(G5531s4)458 


3108 


